[Influences of taurine and micronutrients on nitric oxide synthase expression and cGMP content in rat retina]

AIM

To investigate the influence of taurine and micronutrients on visual signal transmission.

METHODS

Wistar rats were divided into three groups, that is control group, experiment group 1 and experiment group 2, and fed for 3 weeks with normal diet, 5 times and 10 times doses of requirements of taurine, vitamin A, vitamin B, zinc and selenium, then each treatment group were divided into light group and dark adaptation group. After feeding another 3 days in different environments with normal diet, all animals were killed and cGMP level and NOS expression were analysed in retina and retinogeniculate.

RESULTS

The NOS expression and cGMP contents of photoreceptor cells, visual cortex and retinogeniculate were increased in dark adaptation group compared with light group. Nutritional intervention could enhance the NOS staining in dark environment, increased the cGMP contents whether light or dark condition.

CONCLUSION

The distribution, expression and content of NO and cGMP are quite different in various light adaptation status. Taurine and micronutrient intervention may modurate the visual signal transmission or vision function mediated by the changes of NO or cGMP.

A gain-of-function phenotype conferred by over-expression of functional subunits of the COP9 signalosome in Arabidopsis

The COP9 signalosome is a conserved cellular regulator present in diverse organisms. To understand the structural and functional relationship of the COP9 signalosome with its subunits, we expressed in wild-type and mutant Arabidopsis backgrounds two orthologues of subunit 1, rice FUS6 (rFUS6) and human GPS1, and Arabidopsis subunit 8 (COP9). In Arabidopsis, rFUS6 can functionally replace Arabidopsis endogenous FUS6 to form the COP9 signalosome complex and rescue the null fus6-1 mutant phenotype. Moreover, light-grown rFUS6 over-expression seedlings displayed longer hypocotyls and reduced anthocyanin accumulation in comparison to wild-type seedlings, which is opposite to the fus6/cop11 mutant phenotype. The long-hypocotyl phenotype was also observed in transgenic seedlings over-expressing Arabidopsis COP9. This finding indicates that over-expression of a functional subunit 1 or subunit 8 of the COP9 signalosome confers a gain-of-function phenotype relative to the complex. Human GPS1, when expressed in the fus6-1 null mutant of Arabidopsis, can assemble into a chimeric COP9 signalosome at low efficiency, demonstrating the structural conservation of the complexes between human and Arabidopsis. This low-abundancy chimeric complex is insufficient to fully rescue the mutant but is able to attenuate the mutant severity.

Targeted destabilization of HY5 during light-regulated development of Arabidopsis

Arabidopsis seedlings display contrasting developmental patterns depending on the ambient light. Seedlings grown in the light develop photomorphogenically, characterized by short hypocotyls and expanded green cotyledons. In contrast, seedlings grown in darkness become etiolated, with elongated hypocotyls and dosed cotyledons on an apical hook. Light signals, perceived by multiple photoreceptors and transduced to downstream regulators, dictate the extent of photomorphogenic development in a quantitative manner. Two key downstream components, COP1 and HY5, act antagonistically in regulating seedling development. HY5 is a bZIP transcription factor that binds directly to the promoters of light-inducible genes, promoting their expression and photomorphogenic development. COP1 is a RING-finger protein with WD-40 repeats whose nuclear abundance is negatively regulated by light. COP1 interacts directly with HY5 in the nucleus to regulate its activity negatively. Here we show that the abundance of HY5 is directly correlated with the extent of photomorphogenic development, and that the COP1-HY5 interaction may specifically target HY5 for proteasome-mediated degradation in the nucleus.

[Genetic polymorphism of 5 STR loci on chromosome 14 in Chinese Han]

OBJECTIVE

To understand the distribution of genes and genotypes of 5 STR loci on chromosome 14 in Chinese Han.

METHODS

PCR and polyacrylamide gel electrophoresis were used to analyze the polymorphism of 5 STR loci (D14S742, D14S306, D14S606, D14S617, D14S611) on chromosome 14 in Chinese Han.

RESULTS

5 alleles and 13 genotypes, 5 alleles and 13 genotypes, 6 alleles and 13 genotypes, 9 alleles and 21 genotypes, and 6 alleles and 13 genotypes were observed at D14S742, D14S306, D14S606, D14S617 and D14S611, respectively. The frequencies of the most common allele at these five loci were 0.31, 0.31, 0.47, 0.35 and 0.29 respectively.

CONCLUSION

These five loci are highly polymorphic in Chinese Han and their allele distribution is in good agreement with Hardy-Weinberg equilibrium.

Arabidopsis cop8 and fus4 mutations define the same gene that encodes subunit 4 of the COP9 signalosome

The pleiotropic constitutive photomorphogenic/deetiolated/fusca (cop/det/fus) mutants of Arabidopsis exhibit features of light-grown seedlings when grown in the dark. Cloning and biochemical analysis of COP9 have revealed that it is a component of a multiprotein complex, the COP9 signalosome (previously known as the COP9 complex). Here, we compare the immunoaffinity and the biochemical purification of the COP9 signalosome from cauliflower and confirm its eight-subunit composition. Molecular cloning of subunit 4 of the complex revealed that it is a proteasome-COP9 complex-eIF3 domain protein encoded by a gene that maps to chromosome 5, near the chromosomal location of the cop8 and fus4 mutations. Genetic complementation tests showed that the cop8 and fus4 mutations define the same locus, now designated as COP8. Molecular analysis of the subunit 4-encoding gene in both cop8 and fus4 mutants identified specific molecular lesions, and overexpression of the subunit 4 cDNA in a cop8 mutant background resulted in complete rescue of the mutant phenotype. Thus, we conclude that COP8 encodes subunit 4 of the COP9 signalosome. Examination of possible molecular interactions by using the yeast two-hybrid assay indicated that COP8 is capable of strong self-association as well as interaction with COP9, FUS6/COP11, FUS5, and Arabidopsis JAB1 homolog 1, the latter four proteins being previously defined subunits of the Arabidopsis COP9 signalosome. A comparative sequence analysis indicated that COP8 is highly conserved among multicellular eukaryotes and is also similar to a subunit of the 19S regulatory particle of the 26S proteasome.

A magnetic bearing system for a continuous ventricular assist device

This article describes a prototype continuous flow ventricular assist device (CFVAD3) supported in magnetic bearings. The VAD is a small centrifugal four bladed pump. The pump's geometry is explained. The CFVAD3 is the first compact VAD completely supported in magnetic bearings. The magnetic bearings are composed of an inlet side actuator divided into eight pole sets, and an outlet side actuator, also divided into eight pole sets. The pump operating performance was tested and found to be within the design flow rate of up to 9 L/min, and head up to 170 mm Hg for human circulatory support. Magnetic bearing operation out of center positions under various operating orientations were measured and found to be < 1/6 of the bearing clearance, well within specifications. The expected magnetic bearing power loss has been calculated at approximately 6.5 watts.

Characterization of a magnetic bearing system and fluid properties for a continuous flow ventricular assist device

This article presents the performance test results of the CFVAD3 continuous flow blood pump in an artificial human circulation system. The CFVAD3 utilizes magnetic bearings that support a thin pancake impeller, the shape of which allows for a very compact pump whose total axial length is less than 5 cm with a radial length of about 10 cm. This gives a total volume of about 275 cc. The impeller itself has 4 vanes with a designed operating point of 6 L/min at 100 mm Hg of differential pressure and 2,000 rpm. The advantages of magnetic bearings, such as large clearance spaces and no mechanical wear, are elaborated upon. Furthermore, bearing model parameters such as load capacity and current gains are described. These parameters in conjunction with the operating conditions during testing are then used to estimate the fluid forces, stiffness, and damping properties while pumping. Knowledge of these parameters is desirable because of their effects on pump behavior. In addition, a better plant model will allow more robust control algorithms to be devised that can boost pump performance and reliability.

Test controller design, implementation, and performance for a magnetic suspension continuous flow ventricular assist device

A new continuous flow ventricular assist device using full magnetic suspension has been designed, constructed, and tested. The magnetic suspension centers the centrifugal pump impeller within the clearance passages in the pump, thus avoiding any form of contact. The noncontact operation is designed to give very high expected mechanical reliability, large clearances, low hemolysis, and a relatively small size compared to current pulsatile devices. A unique configuration of magnetic actuators on the inlet side and exit sides of the impeller provides full 5 axis control and suspension of the impeller. The bearing system is divided into segments which allow for 3 displacement axes and 2 angular control axes. The controller chosen for the first suspension tests consists of a decentralized set of 5 proportional integral derivative (PID) controllers. This document describes both the controller and an overview of some results pertaining to the magnetic bearing performance. The pump has been successfully operated in both water and blood under design conditions suitable for use as a ventricular assist device.

Evidence for functional conservation of a mammalian homologue of the light-responsive plant protein COP1

Identified in Arabidopsis as a repressor of light-regulated development, the COP1 (constitutively photomorphogenic 1) protein is characterized by a RING-finger motif and a WD40 repeat domain [1]. The subcellular localization of COP1 is light-dependent. COP1 acts within the nucleus to repress photomorphogenic development, but light inactivates COP1 and diminishes its nuclear abundance [2]. Here, we report the identification of a mammalian COP1 homologue that contains all the structural features present in Arabidopsis COP1 (AtCOP1). When expressed in plant cells, a fusion protein comprising mammalian COP1 and beta-glucuronidase (GUS) responded to light by changing its subcellular localization pattern in a manner similar to AtCOP1. Whereas the mammalian COP1 was unable to rescue the defects of Arabidopsis cop1 mutants, expression of the amino-terminal half of mammalian COP1 in Arabidopsis interfered with endogenous COP1 function, resulting in a hyperphotomorphogenic phenotype. Therefore, the regulatory modules in COP1 proteins that are responsible for the signal-dependent subcellular localization are functionally conserved between higher plants and mammals, suggesting that mammalian COP1 may share a common mode of action with its plant counterpart in regulating development and cellular signaling.

Motor feedback physiological control for a continuous flow ventricular assist device

The response of a continuous flow magnetic bearing supported ventricular assist device, the CFVAD3 (CF3) to human physiologic pressure and flow needs is varied by adjustment of the motor speed. This paper discusses a model of the automatic feedback controller designed to develop the required pump performance. The major human circulatory, mechanical, and electrical systems were evaluated using experimental data from the CF3 and linearized models developed. An open-loop model of the human circulatory system was constructed with a human heart and a VAD included. A feedback loop was then closed to maintain a desired reference differential pressure across the system. A proportional-integral (PI) controller was developed to adjust the motor speed and maintain the system reference differential pressure when changes occur in the natural heart. The effects of natural heart pulsatility on the control system show that the reference blood differential pressure is maintained without requiring CF3 motor pulsatility.

Metacarpophalangeal arthroscopy

Although small joint arthroscopy has become commonplace over the past decade, relatively little attention has been paid to the investigation and clinical utility of metacarpophalangeal (MP) joint arthroscopy. The literature is scant in this area and consists of only a handful of case reports. In addition, the arthroscopic anatomy of the MP joint has not as yet been reported. Six cadaveric hands (24 joints) were rigorously studied in the laboratory using standard 2.5-mm small joint arthroscopic instrumentation and 5 lb of overhead traction. Radial and ulnar portals were used with care not to injure the extensor tendons. Arthroscopic anatomic landmarks include: (1) A consistent tripartite configuration of the main radial and ulnar collateral ligaments with characteristic changes in relative fiber orientation as the digit goes from extension to flexion, (2) nonvisualization of the accessory collateral ligament from inside the joint, (3) transitional amorphous capsular fibers connecting the collateral ligaments to the volar plate and dorsal capsule, (4) four synovial recesses (radial, ulnar, volar, and dorsal-proximal), (5) metacarpal head and proximal phalanx, (6) a consistent circumferential meniscal equivalent around the margin of the proximal phalanx articular surface, and (7) the sesamoid-metacarpal articulation in the thumb MPjoint. There are published case reports on the utility of MP joint arthroscopy for synovectomy in rheumatoid arthritis and hemachromatosis and realigning Stener lesions in gamekeepers' thumbs. The current clinical series reveals preliminary experience with the technique. MP joint arthroscopy was useful in relieving a locked MP joint from a loose osteochondral body and sagittal tear in the volar plate that enfolded into the joint surface. Intra-articular release of post-traumatic volar plate and dorsal capsular contracture were readily accomplished using this technique. Juxta-articular bone lesions such as osteoid osteomas can be removed with careful preoperative planning. Gamekeeper's thumbs that are unstable on stress radiographs can undergo arthroscopy with excellent sensitivity to determine the presence of a Stener lesion before an open or arthroscopic repair. The advantages of arthroscopic versus open techniques are similar to those experienced in larger joints. With time, more indications will emerge.

Arthroscopic synovectomy of the metacarpophalangeal joint in refractory rheumatoid arthritis: a technique

Arthroscopic synovectomy was performed on 29 metacarpophalangeal joints belonging to 21 patients with refractory rheumatoid arthritis. This article describes the method of anesthesia, landmarks, and operative technique. Short-term (12-month) results and patient satisfaction have been excellent. No complications were noted. We conclude that arthroscopic synovectomy of the metacarpophalangeal joints in patients with refractory rheumatoid arthritis can be performed safely and effectively. Possibilities for improvement of the technique as well as possible uses of the technique in research are discussed.

Making sense of the COP9 signalosome. A regulatory protein complex conserved from Arabidopsis to human

The COP9 signalosome, once defined as a repressor complex of light-activated development in Arabidopsis, has recently been found in humans and is probably present in most multicellular organisms. The COP9 signalosome is closely related to the lid sub-complex of the 26S proteasome in structural composition and probably shares a common evolutionary ancestor. A multifaceted role of the COP9 signalosome in cell-signaling processes is hinted at by its associated novel kinase activity, as well as the involvement of its subunits in regulating multiple cell-signaling pathways and cell-cycle progression. The molecular genetic studies in Arabidopsis suggest that the complex functions as part of a highly conserved regulatory network, whose physiological role in animals remains to be determined.

Holistic approach to health education on AIDS

OBJECTIVE

To identify a method for health education using the example of an educational seminar on AIDS prevention and control at Hebei Medical University in China, 1994.

METHODS

Our goal is the theoretical formulation of a unified community approach for problem solving through the combination of the self regulative approach and the case analytical approach. "Quality improvement", "essential quality" and "human ecosystems" provide the basic ideas for better understanding the integration of culture, science and technology within the "cultural norm".

RESULTS

The present seminar was successfully organized for Chinese medical students based on the theme of "living with AIDS". Through this program, we identified that self regulative and case analytical approach were major issues for holistic approach to health education. We also identified that a community approach provides the scientific basis for health education in the community.

CONCLUSIONS

The present paper generates a healthcare paradigm for surveillance in health/medical education. Through a better understanding of community approach, we related "community care" (emphasizing self, mutual, professional and institutional care) to the "practical norm"; and "preventive epidemiology" (emphasizing the unification of quality and quantity, as well as systems and population) to the "research norm".

Colonoscopic evaluation of immunochemical fecal occult blood test for detection of colorectal neoplasia

BACKGROUND/AIMS

This study was carried out to assess the validity of three testing methods of immunochemical occult blood according to the number of collection times as a means for colorectal cancer screening.

METHODOLOGY

Four thousand six hundred and eleven asymptomatic individuals, who received both an immunochemical occult blood test with a three-day method and colonoscopy during a medical checkup, served as subjects for this study. For evaluation of the desirable number of sampling times, we used the results of the first day for the 1-day method, the results of the first and second days for the 2-day method, and the results of three-consecutive days for the 3-day method. Sensitivities and specificities of these three testing methods were evaluated.

RESULTS

Sensitivities and specificities for colorectal cancer were calculated to be 56% and 97% for the 1-day method, 83% and 96% for the 2-day method, and 89% and 94% for the 3-day method, respectively, showing a significant difference in sensitivity between the 1-day and the 2-day methods, as well as the 3-day method (p < 0.01), and in specificity between the 1-day as well as the 2-day and 3-day methods (p < 0.05).

CONCLUSIONS

These findings indicate that the immunochemical fecal occult blood test is useful for the diagnosis of colorectal cancer, and that 2-day testing is recommended as a means of screening for colorectal cancer.

S100+ cell response to squamous cell carcinoma of the lip: inverse correlation with metastasis

Previous work has suggested a key role of dendritic cells in antineoplastic immunity. The course of mycosis fungoides and cancers of the lung, colon, thyroid and stomach has been associated with dendritic cell response to the primary tumor. However, this has not been reported for cutaneous or mucosal squamous cell carcinoma (SCC). Thirty-six cases of primary SCC of the lip mucosa or vermillion border, including nine cases with regional metastasis, were studied to investigate the relationship of dendritic cell density with age, tumor grade, mitotic rate, diameter, ulceration, depth of invasion, muscle invasion, tumor-infiltrating lymphocytes (TILs) and metastasis. Dendritic cells were identified using S100 immunohistochemistry, and their peritumor and intratumor density (peri-S100D and intra-S100D) were determined. The mean peri-S100D was 314 +/- 50/mm2. High peri-S100D was associated with lower rate of metastasis (P = 0.03), and no case with peri-S100D > 311/mm2 metastasized. Peri-S100D inversely correlated with depth of invasion (P = 0.04) and ulceration (P = 0.02), and positively associated with TILs (P = 0.02). The mean intra-S100D was 317 +/- 42/mm2. Intra-S100D did not quantitatively correlate with metastasis; however, no metastasis occurred when intra-S100D exceeded 515/mm2. Intra-S100D correlated with brisk TILs (P = 0.04). These results suggest a functional role of dendritic cells in the immune response to SCC. Peri-S100D may be a prognostic indicator.

Reasons for non-compliance in colorectal cancer screening with fecal occult blood test

OBJECTIVES

To identify the reasons for non-compliance with fecal occultblood test in the screening programme for colorectal cancer.

DESIGN AND SETTING

The people who had never participated in the screening programme for colorectal cancer served as the subjects of this study. A structured questionnaire which included the reasons for rejection was sent to each of non-compliers. They were requested to choose two major reasons which were described in a best way that why they did not participate in the programme. The frequency of the stated reasons were analysed from the viewpoint of both sex and age effects.

MAIN RESULTS

A total of 439 people was identified as non-compliers, and 356 (81.1%) people completed the questionnaire. No significant difference was noted in response to the questionnaire between male and female as well as aged 40-59 and those 60-79. The most commonest reason was felt well (47.8%) in male, fear or shyness of further examination (40.2%) in female, and also felt well (48.5%) in aged 40-59, fear or shyness of further examination (40.1%) in aged 60-79. Significant differences were observed in the frequencies of felt well (p<0.01), fear or shyness of further examination (p<0. 01), busy for work (p<0.01) and fear of cancer (p<0.01) between male and female, and also felt well (p<0.01), fear or shyness of further examination (p<0.01), busy for work (p<0.01) and coexistent disease (p<0.01) between aged 40-59 and those 60-79.

CONCLUSIONS

These results suggest that public education about the concept of asymptomatic illness, the benefits of early detection, the safety and painless colonoscopy, and the effective treatment should be emphasised to increase compliance with screening for fecal occult blood.

Characterization and purification of the mammalian COP9 complex, a conserved nuclear regulator initially identified as a repressor of photomorphogenesis in higher plants

The COP9 complex has been identified as a repressor of photomorphogenesis in Arabidopsis. Here we demonstrate that the COP9 complex is also present in mammals. Specific antibodies were generated against human counterparts of the Arabidopsis COP9 and COP11, the two known subunits of plant COP9 complex. Using these antibodies, we showed that indeed mammalian COP9 and COP11, also known as GPS1, could be coimmuno-precipitated using either of the two specific antibodies, definitively confirming that they are physically part of the same complex. Further, the mammalian COP9 and COP11/GPS1 were cofractionated in the same large molecular weight fractions of about 500 kDa and were absent from the monomeric fractions. The mammalian COP9 complex was present in all organs examined but abundances vary. Indirect immunofluorescence studies suggested that the mammalian COP9 complex is largely nuclear localized. Both conventional biochemical and affinity purifications of the COP9 complex from pig spleen indicated that the mammalian COP9 complex consists of eight distinct subunits. These findings indicate that mammals also have a COP9 complex with conserved molecular composition and biochemical and cellular properties similar to the higher plant counterpart.

The COP9 complex is conserved between plants and mammals and is related to the 26S proteasome regulatory complex

The COP9 complex, genetically identified in Arabidopsis as a repressor of photomorphogenesis, is composed of multiple subunits including COP9, FUS6 (also known as COP11) and the Arabidopsis JAB1 homolog 1 (AJH1) ([1-3]; unpublished observations). We have previously demonstrated the existence of the mammalian counterpart of the COP9 complex and purified the complex by conventional biochemical and immunoaffinity procedures [4]. Here, we report the molecular identities of all eight subunits of the mammalian COP9 complex. We show that the COP9 complex is highly conserved between mammals and higher plants, and probably among most multicellular eukaryotes. It is not present in the single-cell eukaryote Saccharomyces cerevisiae, however. All of the subunits of the COP9 complex contain structural features that are also present in the components of the proteasome regulatory complex and the translation initiation factor eIF3 complex. Six subunits of the COP9 complex have overall similarity with six distinct non-ATPase regulatory subunits of the 26S proteasome, suggesting that the COP9 complex and the proteasome regulatory complex are closely related in their evolutionary origin. Subunits of the COP9 complex include regulators of the Jun N-terminal kinase (JNK) and c-Jun, a nuclear hormone receptor binding protein and a cell-cycle regulator. This suggests that the COP9 complex is an important cellular regulator modulating multiple signaling pathways.

Screen compliance rates in 14-years annual screening program for colorectal cancer with immunochemical fecal occult blood test-- identification of higher priority subjects in health education

OBJECTIVES

The present study was carried out to assess compliance rates with annual colorectal cancer screening for fecal occult blood, and to identify the subjects with higher priority in health education to increase screen compliance.

DESIGN AND SETTING

A screening program for colorectal cancer was conducted between 1982 and 1995 in a Japanese villlage. Screen compliance rates in this program were summarised related to sex distribution as well as 10-year age cohorts.

MAIN RESULTS

Screen compliance declined slowly during 14 years time period, and averaged 55.4%. Mean screen compliance was significantly higher in women (56.8%) than in men (53. 8%), and also in aged 50-79 (63.5%) than in aged 50 or less (43.8%), and those 80 and older(12.3%). Subjects who experienced a negative result on colonoscopic examination had significantly lower compliance with screening.

CONCLUSIONS

These findings indicate that the youngest as well as oldest subjects, and the subjects with negative results of fecal occult blood test should be given higher priority in health education to improve screen compliance.

Combinatorial interaction of light-responsive elements plays a critical role in determining the response characteristics of light-regulated promoters in Arabidopsis

We have studied the roles of PhyA, PhyB and CRY1 photoreceptors and the downstream light-signaling components, COP1 and DET1, in mediating high-irradiance light-controlled activity of promoters containing synthetic light-responsive elements (LRE). Promoters with paired LREs were able to respond to a wide spectrum of light through multiple photoreceptors, while the light-inducible single LRE promoters primarily responded to a specific wavelength of light. In addition, our results indicate that Cry1 is involved in PhyB-mediated red-light induction of the G-GATA/NOS101 promoter, and that both Cry1 and PhyB are required for effective repression of the GT1/NOS101 promoter by red or blue light. An interaction between PhyA and PhyB in mediating GT1-GATA/NOS101 promoter light activation was also observed. Furthermore, our data indicate that COP1 and DET1 exert negative control in the dark only on paired LRE promoters but not single LRE promoters. From these results, we conclude that the combinatorial interaction of LREs is essential in determining the ability of light-responsive promoters to be modulated by crucial cellular regulators and to respond to diverse light environments.

Combinatorial interaction of light-responsive elements plays a critical role in determining the response characteristics of light-regulated promoters in Arabidopsis

We have studied the roles of PhyA, PhyB and CRY1 photoreceptors and the downstream light-signaling components, COP1 and DET1, in mediating high-irradiance light-controlled activity of promoters containing synthetic light-responsive elements (LRE). Promoters with paired LREs were able to respond to a wide spectrum of light through multiple photoreceptors, while the light-inducible single LRE promoters primarily responded to a specific wavelength of light. In addition, our results indicate that Cry1 is involved in PhyB-mediated red-light induction of the G-GATA/NOS101 promoter, and that both Cry1 and PhyB are required for effective repression of the GT1/NOS101 promoter by red or blue light. An interaction between PhyA and PhyB in mediating GT1-GATA/NOS101 promoter light activation was also observed. Furthermore, our data indicate that COP1 and DET1 exert negative control in the dark only on paired LRE promoters but not single LRE promoters. From these results, we conclude that the combinatorial interaction of LREs is essential in determining the ability of light-responsive promoters to be modulated by crucial cellular regulators and to respond to diverse light environments.

Arabidopsis bZIP protein HY5 directly interacts with light-responsive promoters in mediating light control of gene expression

The Arabidopsis HY5 gene has been defined genetically as a positive regulator of photomorphogenesis and recently has been shown to encode a basic leucine zipper type of transcription factor. Here, we report that HY5 is constitutively nuclear localized and is involved in light regulation of transcriptional activity of the promoters containing the G-box, a well-characterized light-responsive element (LRE). In vitro DNA binding studies suggested that HY5 can bind specifically to the G-box DNA sequences but not to any of the other LREs present in the light-responsive promoters examined. High-irradiance light activation of two synthetic promoters containing either the consensus G-box alone or the G-box combined with the GATA motif (another LRE) and the native Arabidopsis ribulose bisphosphate carboxylase small subunit gene RBCS-1A promoter, which has an essential copy of the G-box, was significantly compromised in the hy5 mutant. The hy5 mutation's effect on the high-irradiance light activation of gene expression was observed in both photosynthetic and nonphotosynthetic tissues. Furthermore, the characteristic phytochrome-mediated red light- and far-red light-reversible low-fluence induction of the G-box-containing promoters was diminished specifically in hy5 plants. These results suggest that HY5 may interact directly with the G-box in the promoters of light-inducible genes to mediate light-controlled transcriptional activity.

Molecular interaction between COP1 and HY5 defines a regulatory switch for light control of Arabidopsis development

Arabidopsis COP1 acts as a light-inactivable repressor of photomorphogenic development, but its molecular mode of action remains unclear. Here, we show that COP1 negatively regulates HY5, a bZIP protein and a positive regulator of photomorphogenic development. Both in vitro and in vivo assays indicate that COP1 interacts directly and specifically with HY5. The hyperphotomorphogenic phenotype caused by the over-expression of a mutant HY5, which lacks the COP1-interactive domain, supports the regulatory role of HY5-COP1 interaction. Further, HY5 is capable of directly interacting with the CHS1 minimal promoter and is essential for its light activation. We propose that the direct interaction with and regulation of transcription factors by COP1 may represent the molecular mechanism for its control of gene expression and photomorphogenic development.

A unique intronic splicing enhancer controls the inclusion of the agrin Y exon

Alternative splicing of the agrin mRNA controls the ability of agrin protein to induce the clustering of acetylcholine receptors at the neuromuscular junction. Using a transfectable reporter gene, we show that one agrin alternative exon, the Y exon, is controlled by a regulatory sequence in the downstream intron. Portions of this intronic sequence have the properties of a splicing enhancer that can activate splicing of a heterologous exon when placed in the intron downstream. The regulatory region is complex in structure, containing several different elements capable of activating splicing. Individual enhancing elements differ in their cell-type specificity, and are not apparently synergistic, as two elements together induce lower splicing than either does separately. Essential nucleotides within these regulatory elements were identified by scanning mutagenesis across the active region. Interestingly, the elements do not appear similar to known intronic splicing enhancer elements. This Y exon enhancer and its components take part in an apparent combinatorial system of control where multiple regulatory elements of varying activity combine to produce a precisely cell-specific exon inclusion. As a major contributor to the regulation of the Y exon, the enhancer ultimately controls the properties of the agrin protein.

The holmium YAG laser in office based arthroscopy of the knee: comparison with standard interventional instruments in patients with arthritis

OBJECTIVE

To confirm the feasibility of laser assisted technology in an office based rheumatology practice and to compare selected outcome variables with those of conventional arthroscopic cutting tools.

METHODS

A prospective analysis of 70 office based arthroscopies on 70 patients with knee arthritis over an 8 month period. All patients met specific criteria for office based arthroscopy. Thirty-six patients had interventions with conventional cutting tools and 34 patients had interventions with a 40 watt holmium YAG laser. Variables assessed included procedure time, length of recuperative period, and postprocedural pain.

RESULTS

Laser assisted arthroscopy was performed in 34 cases without side effects or complications. Patients who received laser treatment had a shorter recuperative period, less postprocedural pain, and fewer hemarthroses than patients treated with conventional methods.

CONCLUSION

While recognizing the shortcomings and possible complications associated with laser surgery, we conclude that laser use in an office setting is not only feasible but may in the future be an excellent method for office based arthroscopic treatment of the arthritic knee.

Expression of vascular endothelial growth factor in synovial fibroblasts is induced by hypoxia and interleukin 1beta

OBJECTIVE

To study the mechanism by which hypoxia and inflammatory cytokines mediate angiogenesis in the rheumatoid pannus through their effects on the fibroblast-like type B synoviocyte, the major cell type of normal synovia.

METHODS

Fibroblasts were prepared from synovial tissue of healthy and diseased individuals, and cultured in the presence of various stimuli. The expression of vascular endothelial growth factor (VEGF) was assessed by ELISA and reverse transcription polymerase chain reaction.

RESULTS

Unlike normal fibroblasts, synovial fibroblasts from rheumatoid arthritis (RA) and osteoarthritis constitutively secreted significant levels of VEGF, which is known to act directly on endothelial cells. VEGF secretion was further inducible by both hypoxia and interleukin 1beta (IL-1beta) and these increases were additive. In contrast, tumor necrosis factor alpha was unable to induce VEGF expression.

CONCLUSION

Under hypoxia or IL-1 stimulation, conditions common to the inflamed synovium, type B synoviocytes secrete increased levels of VEGF, which is likely to act on nearby endothelia, promoting angiogenesis. The constitutive expression of VEGF in rheumatoid synovial fibroblasts may reflect an altered phenotype involved in the pathology of RA.

Evidence for FUS6 as a component of the nuclear-localized COP9 complex in Arabidopsis

The pleiotropic CONSTITUTIVE PHOTOMORPHOGENIC (COP), DEETIOLATED (DET), and FUSCA (FUS) loci are essential regulatory genes involved in the light control of seedling developmental patterns in Arabidopsis. Although COP1, DET1, COP9, and FUS6 (also called COP11) have been cloned, their biochemical activities and interactions remain elusive. We have recently suggested that multiple pleiotropic COP, DET, and FUS genes may encode subunits of a large regulatory complex. In this study, we generated specific antibodies against Arabidopsis FUS6 and show that accumulation of both COP9 and FUS6 is coordinated in the pleiotropic cop, det, and fus mutant backgrounds and in wild-type plants throughout development. Both COP9 and FUS6 cofractionated into identical high molecular mass fractions in an analytical gel filtration assay, and neither was found in its monomeric form. Moreover, antibodies raised against either COP9 or FUS6 selectively coimmunoprecipitated both proteins. We have also developed an Arabidopsis protoplast immunolocalization assay and demonstrated that the COP9 complex is localized in the nucleus and that its nuclear localization is not affected by light conditions or tissue types. The integrated genetic and biochemical results strongly support the conclusion that both COP9 and FUS6 are components of the nuclear-localized COP9 complex. Therefore, we have provided the strongest evidence for the conclusion that at least some of the pleiotropic COP, DET, and FUS loci act in the same signaling pathway.

Combinatorial interplay of promoter elements constitutes the minimal determinants for light and developmental control of gene expression in Arabidopsis

Higher plants are able to integrate environmental and endogenous signals to regulate gene expression for optimal development. To define the minimal sequence requirement sufficient to integrate light and developmental signals in controlling promoter activity, we carried out a systematic analysis of the roles of four well-conserved 'light-responsive elements (LREs)' common to many nuclear-encoded photosynthetic genes. A gain-of-function assay using basal promoter-reporter fusions in stable transgenic Arabidopsis was employed to demonstrate that pairwise combinations of the LREs, but not the individual elements alone, can confer light-inducible expression to the reporter gene independently of the basal promoter context and the light-triggered morphological changes. The activity of the synthetic promoters with the paired LREs can be modulated at least by the phytochrome system. Further, those synthetic light-regulated promoters confer a photosynthetic cell-specific expression pattern and respond to the chloroplast development state. Our data suggest that distinct combinatorial interactions of LREs can serve as minimal autonomous promoter determinants which integrate light and developmental signals and modulate promoter activity.

The COP9 complex, a novel multisubunit nuclear regulator involved in light control of a plant developmental switch

Arabidopsis COP9 is a component of a large protein complex that is essential for the light control of a developmental switch and whose conformation or size is modulated by light. The complex is acidic, binds heparin, and is localized within the nucleus. Biochemical purification of the complex to near homogeneity revealed that it contains 12 distinct subunits. One of the other subunits is COP11, mutations in which result in a phenotype identical to cop9 mutants. The COP9 complex may act to regulate the nuclear abundance of COP1, an established repressor of photomorphogenic development. During the biogenesis of the COP9 complex, a certain degree of prior subunit association is a prerequisite for proper nuclear translocation. Since both COP9 and COP11 have closely related human counterparts, the COP9 complex probably represents a conserved developmental regulator in higher eukaryotes.

Vesnarinone is a selective inhibitor of macrophage TNF(alpha) release

Vesnarinone is an experimental drug that has been used successfully in the treatment of congestive heart failure patients. In this report we investigate the effect of vesnarinone on the cytokine secretory products of mononuclear phagocytes. In a concentration-dependent manner, the drug inhibits the endotoxin(LPS)-stimulated release of tumor necrosis factor (TNF) alpha and suppresses interleukin(IL)-6 release, but does not affect the release of IL-1 alpha, IL-10 and leukemia inhibitory factor (LIF) by mouse peritoneal macrophages. Using competitive polymerase chain reaction (PCR) analyses, we find that vesnarinone significantly reduces TNF(alpha), but not IL-10 mRNA. In addition to LPS, the drug inhibits TNF(alpha) release induced by several other stimuli. The inhibitory effect of the drug on the TNF(alpha) biosynthesis can be observed in differentiated human monocytes, in macrophage cell lines, and in synovial adherent cells from rheumatoid arthritis patients. Although the precise mode of action of vesnarinone in the signal transduction pathway leading to the selective inhibition of TNF(alpha) is not known, the drug might be useful in the treatment of diseases involving that cytokine.

Complications of office based arthroscopy of the knee

OBJECTIVE

To analyze the complication rates associated with office based arthroscopy in 2 community based rheumatology practices.

METHODS

A retrospective analysis of 335 office based arthroscopy performed on 306 patients over a 35 mo period. All patients met specific clinical criteria to qualify for office based arthroscopy. Patients were followed postarthroscopy for a minimum of 12 weeks to assess the rates and types of complications.

RESULTS

Of the 335 office based arthroscopies, 131 were diagnostic only, while 204 procedures were diagnostic and therapeutic. A total of 280 interventions were performed. Both major and minor complications were seen. The complication rates for major and minor events were 1.2 and 12.8%, respectively. There was no mortality or longterm morbidity.

CONCLUSION

Office based arthroscopy in patients with rheumatic diseases has a safety profile that compares favorably with arthroscopy performed in an ambulatory surgical center or operating room setting.

Immunodetection, expression strategy and complementation of turnip crinkle virus p28 and p88 replication components

The plus-sense RNA genome of turnip crinkle virus (TCV) encodes at its 5' end a 28-kDa protein of unspecified function. Readthrough suppression of the p28 stop codon allows for the production of an 88-kDa product which is required for genome replication. Immunological analysis of the expression of p28 and p88 demonstrated that: (i) the genome directs the synthesis of polypeptides of approximately 28 and 88 kDa, (ii) the 88-kDa protein is immunologically related to p28, consistent with p88 being a readthrough product, and (iii) p28, but not p88, is detectable in vivo. An in vivo assay, in which readthrough is linked to the expression of a beta-glucuronidase reporter gene, showed that readthrough of the p28 amber stop codon occurs with an efficiency of approximately 1%. A similar efficiency of readthrough was observed when an altered context from the nonviable TCV mutant, mA2, containing a disrupted secondary structure (FfFa) spanning the p28 termination codon, was tested. This result suggests that the defective phenotype of mA2 is likely not linked to an alteration in readthrough efficiency. Additional studies demonstrated that complementation occurs in coinoculations with two nonviable TCV mutants, RT and APA, which are unable to express either p28 or p88, respectively. This result verifies that p28 is essential for TCV genome replication and provides the first definitive evidence for the role of a 5'-proximal open reading frame for any member of the family Tombusviridae.

Arabidopsis COP1 protein specifically interacts in vitro with a cytoskeleton-associated protein, CIP1

Arabidopsis COP1 acts inside the nucleus to suppress photomorphogenic cellular development, and light inactivation of COP1 may involve a specific control of its nuclear activity in hypocotyls and cotyledons, but not in roots, of developing seedlings. To understand the molecular mechanisms of COP1 action during light-mediated development, we initiated a screen for Arabidopsis cDNAs encoding proteins which interact directly with COP1 in vitro as a step to identify the cellular components involved. We report here the isolation and characterization of a cDNA clone encoding a protein designated CIP1 (COP1-interactive protein 1). CIP1 is predominantly alpha-helical and most likely involved in coiled-coil formation. It interacts specifically with the putative coiled-coil region of COP1 in vitro. Further, CIP1 is encoded by a single gene in Arabidopsis, and its mRNA and protein levels are not regulated by light. Immunofluorescent labeling of CIP1 in Arabidopsis seedling protoplasts demonstrated that CIP1 is part of, or associated with, a cytoskeletal structure in hypocotyl and cotyledon cells, but not in roots. Our results are consistent with a possible role of CIP1 in mediating light control of COP1 nuclear activity by regulating its nucleocytoplasmic partitioning.

Measurement of secretogranin II release from individual adenohypophysial gonadotropes

Secretogranin II (SG-II) is an acidic 86-kDa protein found in high abundance in the anterior pituitary gland. In the present studies, we investigated the secretion and the localization of SG-II using pituitary cells from female rats at all stages of the estrous cycle. Double immunofluorescence staining revealed that SG-II immunoreactivity was localized in low abundance in about half of all pituitary cells and in high abundance in all of the luteinizing hormone (LH)-immunoreactive cells (which represent approximately 5% of all pituitary cells). Using a reverse hemolytic plaque assay for measurement of SG-II release from individual pituitary cells in culture, we found that SG-II secretion was strongly stimulated by gonadotropin-releasing hormone in a dose-related fashion, and the amount of SG-II secretion was also related to the stage of the estrous cycle: it was highest at proestrus and lowest at estrus. SG-II plaque assay followed by LH immunofluorescence staining further revealed that all the SG-II-secreting cells contained LH immunoreactivity. At proestrus all the LH-immunoreactive cells secreted SG-II, whereas another days of the estrous cycle only a fraction of them did so. Thus our findings demonstrate a striking resemblance between SG-II and LH with regard to cell localization and secretory regulation.

Stress fractures of the distal fibula presenting as monarticular flares in patients with rheumatoid arthritis

Monarticular flares occurring in patients with rheumatoid arthritis (RA) usually signify either a worsening of the underlying condition or a superimposed septic process. This report describes 2 patients with RA who had stress fractures of the fibular head, masquerading as monarticular flares of ankle arthritis.

Enhancement of hemin-induced membrane damage by artemisinin

Artemisinin is an effective antimalarial agent, and its action on the malarial parasite is suggested to be mediated by oxidative processes. Since malarial parasites contain a high concentration of hemin, and hemin may induce the formation of reactive oxygen species, we investigated the interaction of artemisinin, iron and hemin. We used erythrocyte membrane-bound Ca2+ pump ATPase (basal) and calmodulin (CaM)-activated Ca2+ pump ATPase as our model. Membranes were incubated with artemisinin in the presence or absence of iron-ascorbate or hemin at 37 degrees for 1 hr. Following incubation, ATPase activity was measured. Our results showed that artemisinin (500 microM) had no effect on ATPase activities. However, artemisinin enhanced the inhibitory effect of iron (50 microM)-ascorbate (500 microM) on ATPase activity (46.3 +/- 3.9 vs 63 +/- 2.1% for basal; 57.2 +/- 2.5 vs 74.8 +/- 2.1% for CaM-activated). Desferrioxamine (DFO, 200 microM) blocked significantly the effect of iron-ascorbate-artemisinin on ATPases (P < 0.01). Hemin inhibited ATPase activity in a concentration-dependent fashion. Artemisinin enhanced hemin (10 microM)-induced inhibition of basal (36.0 +/- 6.0 vs 73.7 +/- 3.0%) and CaM-activated Ca2+ pump ATPase (31.6 +/- 2.8 vs 70.0 +/- 1.5%). Iron chelators (DFO, ferene, 8-hydroxyquinoline, 1,10-phenanthroline, and 1,2-dimethyl-3-hydroxypyrid-4-one) had no effect on artemisinin plus hemin-induced enzyme inhibition. Catalase (2000 U/mL) had a minor effect on the artemisinin-hemin or hemin-mediated effect. Thiourea (1 mM) had no effect. However, superoxide dismutase (500 U/mL) and dithiothreitol blocked artemisinin-hemin or hemin-mediated ATPase inhibition significantly (P < 0.001). In conclusion, these results suggest that, in our model, artemisinin enhances the damage of hemin-induced ATPases via oxidation of thiol groups on the enzymes. Free iron or hydroxyl radical does not seem to be involved. This interaction between artemisinin and hemin may contribute to the antimalarial action of artemisinin against malarial parasites.

Arabidopsis COP9 is a component of a novel signaling complex mediating light control of development

Environmental light signals are sensed by multiple families of photoreceptors and transduced by largely unknown mechanisms to regulate plant development. In this report, genetic analysis suggested that light signals perceived by both phytochromes and a blue light receptor converge to repress the action of Arabidopsis COP9 in suppressing seedling photomorphogenesis. Molecular cloning of the gene revealed that COP9 encodes a novel protein of 197 amino acids whose expression is not regulated by light. COP9 functions as a large (> 560 kDa) complex(es) that is probably subjected to light modulation. In addition, COP8 and COP11 are required for either the COP9 complex formation or its stability. Therefore COP9, together with COP8 and COP11, defines a novel signaling step in mediating light control of plant development.

Arabidopsis COP8, COP10, and COP11 genes are involved in repression of photomorphogenic development in darkness

Wild-type Arabidopsis seedlings are capable of following two developmental programs: photomorphogenesis in the light and skotomorphogenesis in darkness. Screening of Arabidopsis mutants for constitutive photomorphogenic development in darkness resulted in the identification of three new loci designated COP8, COP10, and COP11. Detailed examination of the temporal morphological and cellular differentiation patterns of wild-type and mutant seedlings revealed that in darkness, seedlings homozygous for recessive mutations in COP8, COP10, and COP11 failed to suppress the photomorphogenic developmental pathway and were unable to initiate skotomorphogenesis. As a consequence, the mutant seedlings grown in the dark had short hypocotyls and open and expanded cotyledons, with characteristic photomorphogenic cellular differentiation patterns and elevated levels of light-inducible gene expression. In addition, plastids of dark-grown mutants were defective in etioplast differentiation. Similar to cop1 and cop9, and in contrast to det1 (deetiolated), these new mutants lacked dark-adaptive change of light-regulated gene expression and retained normal phytochrome control of seed germination. Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well. Further, cop8-1, cop10-1, and cop11-1 mutants accumulated higher levels of COP1, a feature similar to the cop9-1 mutant. These results suggested that COP8, COP10, and COP11, together with COP1, COP9, and DET1, function to suppress the photomorphogenic developmental program and to promote skotomorphogenesis in darkness. The identical phenotypes resulting from mutations in COP8, COP9, COP10, and COP11 imply that their encoded products function in close proximity, possibly with some of them as a complex, in the same signal transduction pathway.

Arabidopsis COP8, COP10, and COP11 genes are involved in repression of photomorphogenic development in darkness

Wild-type Arabidopsis seedlings are capable of following two developmental programs: photomorphogenesis in the light and skotomorphogenesis in darkness. Screening of Arabidopsis mutants for constitutive photomorphogenic development in darkness resulted in the identification of three new loci designated COP8, COP10, and COP11. Detailed examination of the temporal morphological and cellular differentiation patterns of wild-type and mutant seedlings revealed that in darkness, seedlings homozygous for recessive mutations in COP8, COP10, and COP11 failed to suppress the photomorphogenic developmental pathway and were unable to initiate skotomorphogenesis. As a consequence, the mutant seedlings grown in the dark had short hypocotyls and open and expanded cotyledons, with characteristic photomorphogenic cellular differentiation patterns and elevated levels of light-inducible gene expression. In addition, plastids of dark-grown mutants were defective in etioplast differentiation. Similar to cop1 and cop9, and in contrast to det1 (deetiolated), these new mutants lacked dark-adaptive change of light-regulated gene expression and retained normal phytochrome control of seed germination. Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well. Further, cop8-1, cop10-1, and cop11-1 mutants accumulated higher levels of COP1, a feature similar to the cop9-1 mutant. These results suggested that COP8, COP10, and COP11, together with COP1, COP9, and DET1, function to suppress the photomorphogenic developmental program and to promote skotomorphogenesis in darkness. The identical phenotypes resulting from mutations in COP8, COP9, COP10, and COP11 imply that their encoded products function in close proximity, possibly with some of them as a complex, in the same signal transduction pathway.

The p21 Cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases

The cyclin-dependent kinase Cdk2 associates with cyclins A, D, and E and has been implicated in the control of the G1 to S phase transition in mammals. To identify potential Cdk2 regulators, we have employed an improved two-hybrid system to isolate human genes encoding Cdk-interacting proteins (Cips). CIP1 encodes a novel 21 kd protein that is found in cyclin A, cyclin D1, cyclin E, and Cdk2 immunoprecipitates. p21CIP1 is a potent, tight-binding inhibitor of Cdks and can inhibit the phosphorylation of Rb by cyclin A-Cdk2, cyclin E-Cdk2, cyclin D1-Cdk4, and cyclin D2-Cdk4 complexes. Cotransfection experiments indicate that CIP1 and SV40 T antigen function in a mutually antagonistic manner to control cell cycle progression.

Regulation of expression of secretogranin II mRNA in female rat pituitary and hypothalamus

Secretogranin II (SgII) is an acidic 86-kD protein which is synthesized by most neuroendocrine cells but occurs in greatest abundance in the anterior pituitary gland where it is localized primarily in gonadotrophs. In the present studies, we investigated the regulation of SgII mRNA expression in the anterior pituitary gland by estrogens and gonadotropin-releasing hormone (GnRH) and compared the results to luteinizing hormone beta-subunit (LH beta) mRNA expression. Molecular cloning and nucleotide sequence analysis of a rat pituitary SgII cDNA revealed a derived amino acid sequence identical with that previously reported for the rat adrenal. Not previously reported were five putative nuclear localization signals, four of which coincided with dibasic residues previously thought to serve as proteolytic cleavage sites. In Northern blots, SgII mRNA was found in high abundance in the anterior pituitary gland, in moderate abundance in the brain and adrenal, and in low abundance in the ovary and testis. Measurements of pituitary SgII mRNA during the rat 4-day estrous cycle revealed an inverse relationship with LH beta mRNA: SgII mRNA decreased, whereas LH beta mRNA increased as the cycle progressed. Increases in pituitary SgII mRNA and LH beta mRNA levels occurred after ovariectomy, and decreases occurred after estrogen treatment of such animals. Likewise, pituitary SgII mRNA and LH beta mRNA levels decreased after treatment of ovariectomized animals with a GnRH antagonist. In contrast, ovariectomy significantly decreased SgII mRNA levels in the hypothalamus, and estrogen treatment increased its levels. Our studies reveal that ovarian estrogens and hypothalamic GnRH exert similar effects on SgII mRNA and LH beta mRNA expression in the pituitary. However, since their expression is inverse during the rat estrous cycle, other unidentified regulatory factors with differential effects on their expression may intervene in the regulation of SgII and LH beta mRNA levels.

Phosphorylation independent activation of human cyclin-dependent kinase 2 by cyclin A in vitro

p33cdk2 is a serine-threonine protein kinase that associates with cyclins A, D, and E and has been implicated in the control of the G1/S transition in mammalian cells. Recent evidence indicates that cyclin-dependent kinase 2 (Cdk2), like its homolog Cdc2, requires cyclin binding and phosphorylation (of threonine-160) for activation in vivo. However, the extent to which mechanistic details of the activation process are conserved between Cdc2 and Cdk2 is unknown. We have developed bacterial expression and purification systems for Cdk2 and cyclin A that allow mechanistic studies of the activation process to be performed in the absence of cell extracts. Recombinant Cdk2 is essentially inactive as a histone H1 kinase (< 4 x 10(-5) pmol phosphate transferred.min-1 x microgram-1 Cdk2). However, in the presence of equimolar cyclin A, the specific activity is approximately 16 pmol.mon-1 x microgram-1, 4 x 10(5)-fold higher than Cdk2 alone. Mutation of T160 in Cdk2 to either alanine or glutamic acid had little impact on the specific activity of the Cdk2/cyclin A complex: the activity of Cdk2T160E was indistinguishable from Cdk2, whereas that of Cdk2T160A was reduced by five-fold. To determine if the Cdk2/cyclin A complex could be activated further by phosphorylation of T160, complexes were treated with Cdc2 activating kinase (CAK), purified approximately 12,000-fold from Xenopus eggs. This treatment resulted in an 80-fold increase in specific activity. This specific activity is comparable with that of the Cdc2/cyclin B complex after complete activation by CAK (approximately 1600 pmol.mon-1 x microgram-1). Neither Cdk2T160A/cyclin A nor Cdk2T160E/cyclin A complexes were activated further by treatment with CAK. In striking contrast with cyclin A, cyclin B did not directly activate Cdk2. However, both Cdk2/cyclin A and Cdk2/cyclin B complexes display similar activity after activation by CAK. For the Cdk2/cyclin A complex, both cyclin binding and phosphorylation contribute significantly to activation, although the energetic contribution of cyclin A binding is greater than that of T160 phosphorylation by approximately 5 kcal/mol. The potential significance of direct activation of Cdk2 by cyclins with respect to regulation of cell cycle progression is discussed.

COP9: a new genetic locus involved in light-regulated development and gene expression in arabidopsis

We report here the identification and characterization of a new Arabidopsis light-regulatory locus, COP9, mutation that leads to a constitutive photomorphogenic phenotype. Dark-grown cop9 seedlings exhibit many morphological characteristics of light-grown seedlings, including short hypocotyls and open and enlarged cotyledons with cell-type and chloroplast differentiation. Furthermore, the cop9 mutation leads to high-level expression of light-inducible genes in the absence of light, probably by altering the promoter activities of these genes. These properties imply that the mutation in the COP9 locus uncouples the light/dark signals from morphogenesis and light-regulated gene expression. In addition, light-grown cop9 mutants are severely dwarfed and are unable to reach maturation and flowering. This adult-lethal phenotype indicates that the COP9 locus also plays a critical role for normal development of the light-grown plant. Similar to cop1 mutants, but not det1, the cop9 mutants show (1) no effect on the phytochrome control of seed germination and (2) deficiency in the dark-adaptive change of expression of light-regulated genes. Our results suggest that the cop9 and cop1 mutations result in the same range of phenotypes and therefore COP9 and COP1 loci may encode closely related components in the same regulatory pathway.