A multi-isotope approach reveals seasonal variation in the reliance on marine resources, production of metabolic water, and ingestion of seawater by two species of coastal passerine to maintain water balance

Tracing how free-ranging organisms interact with their environment to maintain water balance is a difficult topic to study for logistical and methodological reasons. We use a novel combination of triple-oxygen stable isotope analyses of water extracted from plasma (δ16O, δ17O, δ18O) and bulk tissue carbon (δ13C) and nitrogen (δ15N) isotopes of feathers and blood to estimate the proportional contribution of marine resources, seawater, and metabolic water used by two species of unique songbirds (genus Cinclodes) to maintain their water balance in a seasonal coastal environment. We also assessed the physiological adjustments that these birds use to maintain their water balance. In agreement with previous work on these species, δ13C and δ15N data show that the coastal resident and invertivore C. nigrofumosus consumes a diet rich in marine resources, while the diet of migratory C. oustaleti shifts seasonally between marine (winter) to freshwater aquatic resources (summer). Triple-oxygen isotope analysis (Δ17O) of blood plasma, basal metabolic rate (BMR), and total evaporative water loss (TEWL) revealed that ~25% of the body water pool of both species originated from metabolic water, while the rest originated from a mix of seawater and fresh water. Δ17O measurements suggest that the contribution of metabolic water tends to increase in summer in C. nigrofumosus, which is coupled with a significant increase in BMR and TEWL. The two species had similar BMR and TEWL during the austral winter when they occur sympatrically in coastal environments. We also found a positive and significant association between the use of marine resources as measured by δ13C and δ15N values and the estimated δ18O values of ingested (pre-formed) water in both species, which indicates that Cinclodes do not directly drink seawater but rather passively ingest when consuming marine invertebrates. Finally, results obtained from physiological parameters and the isotope-based estimates of marine (food and water) resource use are consistent, supporting the use of the triple-oxygen isotopes to quantify the contribution of water sources to the total water balance of free-ranging birds.

Triple Oxygen Isotope Measurements (Δ'17O) of Body Water Reflect Water Intake, Metabolism, and δ18O of Ingested Water in Passerines

Understanding physiological traits and ecological conditions that influence a species reliance on metabolic water is critical to creating accurate physiological models that can assess their ability to adapt to environmental perturbations (e.g., drought) that impact water availability. However, relatively few studies have examined variation in the sources of water animals use to maintain water balance, and even fewer have focused on the role of metabolic water. A key reason is methodological limitations. Here, we applied a new method that measures the triple oxygen isotopic composition of a single blood sample to estimate the contribution of metabolic water to the body water pool of three passerine species. This approach relies on Δ'¹⁷O, defined as the residual from the tight linear correlation that naturally exists between δ¹⁷O and δ¹⁸O values. Importantly, Δ'17O is relatively insensitive to key fractionation processes, such as Rayleigh distillation in the water cycle that have hindered previous isotope-based assessments of animal water balance. We evaluated the effects of changes in metabolic rate and water intake on Δ'¹⁷O values of captive rufous-collared sparrows (Zonotrichia capensis) and two invertivorous passerine species in the genus Cinclodes from the field. As predicted, colder acclimation temperatures induced increases in metabolic rate, decreases in water intake, and increases in the contribution of metabolic water to the body water pool of Z. capensis, causing a consistent change in Δ'¹⁷O. Measurement of Δ'¹⁷O also provides an estimate of the δ¹⁸O composition of ingested pre-formed (drinking/food) water. Estimated δ¹⁸O values of drinking/food water for captive Z. capensis were ~ −11‰, which is consistent with that of tap water in Santiago, Chile. In contrast, δ¹⁸O values of drinking/food water ingested by wild-caught Cinclodes were similar to that of seawater, which is consistent with their reliance on marine resources. Our results confirm the utility of this method for quantifying the relative contribution of metabolic versus pre-formed drinking/food water to the body water pool in birds.

Relating Δ17O Values of Animal Body Water to Exogenous Water Inputs and Metabolism

The dynamics of animal body water and metabolism are integral aspects of biological function but are difficult to measure, particularly in free-ranging individuals. We demonstrate a new method to estimate inputs to body water via analysis of Δ17O, a measure of 17O/16O relative to 18O/16O. Animal body water is primarily a mixture of drinking or food water (meteoric water; Δ17O ≈ 0.030 per mille [‰]) and metabolic water synthesized from atmospheric oxygen (Δ17O ≈ –0.450‰). Greater drinking or food water intake should increase Δ17O toward 0.030‰, whereas greater metabolic rate should decrease Δ17O toward –0.450‰. We found that wild mammal Δ17O values generally increased with body mass, consistent with both a decline in mass-specific metabolic rate and an increase in water intake. Captive mouse (Peromyscus maniculatus) Δ17O values were higher than predicted but exhibited the expected relative change based on metabolic rate and water intake. Measurements of Δ17O may enable novel ecophysiological studies.

Measurement of Adjuncts in Hard Ciders Obtainable in the United States Using Carbon Isotopes

The carbon isotope compositions (δ¹³C values) of 23 hard ciders obtainable in the United States were analyzed to detect adjuncts, specifically added C₄ sugars (i.e., corn syrup and cane sugar). In contrast, the main ingredient of hard ciders is fruit, mostly apple, juice which is derived from C₃ plants. The labeled ingredients of ciders were found to be inconsistent with the carbon isotope ratios. A higher proportion of imported ciders studied had no isotopic evidence of added C₄-based sweetener, while most domestic ciders had elevated δ¹³C values, indicative of C₄-based sugar additives. European ciders could contain beet sugar, a common sweetener used in that region, which would not be detected as an additive because it is a C₃-based sweetener. The δ¹³C values of the ciders were found to have no correlation with the amount of sugar in the cider, as reported on the nutritional information label, likely reflecting varying fermentation times. An increase in the amount of added C₄ sugars did not correspond to a decrease in price, in contrast to what is found in beers.

Nitrogen recycling at the Costa Rican subduction zone: The role of incoming plate structure

Efficient recycling of subducted sedimentary nitrogen (N) back to the atmosphere through arc volcanism has been advocated for the Central America margin while at other locations mass balance considerations and N contents of high pressure metamorphic rocks imply massive addition of subducted N to the mantle and past the zones of arc magma generation. Here, we report new results of N isotope compositions with gas chemistry and noble gas compositions of forearc and arc front springs in Costa Rica to show that the structure of the incoming plate has a profound effect on the extent of N subduction into the mantle. N isotope compositions of emitted arc gases (9-11 N°) imply less subducted pelagic sediment contribution compared to farther north. The N isotope compositions (δ¹⁵N = -4.4 to 1.6‰) of forearc springs at 9-11 N° are consistent with previously reported values in volcanic centers (δ¹⁵N = -3.0 to 1.9‰). We advocate that subduction erosion enhanced by abundant seamount subduction at 9-11 N° introduces overlying forearc crustal materials into the Costa Rican subduction zone, releasing fluids with lighter N isotope signatures. This process supports the recycling of heavier N into the deep mantle in this section of the Central America margin.

The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest

From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO₂ concentrations from 270 to 400 mol mol^-1 . The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of free-air CO₂ enrichment (FACE) experiments. These experiments have found (i) an increase in internal CO₂ partial pressure (c_i ) alongside acclimation of photosynthetic capacity, (ii) variable decreases in stomatal conductance, and (iii) that increases in yield do not increase commensurate with CO₂ concentrations. Our data set, which includes a 115-year-long selection of grasses collected in New Mexico since 1892, is consistent with an increased c_i as a response to historical CO₂ increase in the atmosphere, with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity Index (PDSI) for New Mexico indicates a moderate correlation with Δ¹³ C (r²  = 0.32, P < 0.01) before 1950, with no correlation (r²  = 0.00, P = 0.91) after 1950. These results indicate that increased c_i may have conferred some drought resistance to these grasses through increased availability of CO₂ in the event of reduced stomatal conductance in response to short-term water shortage. Comparison with C₃ trees from arid environments (Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments (Bromus and Poa grasses in New Mexico) suggests differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO₂ while wetter environments see increased c_i . This study suggests that (i) the observed increases in c_i in FACE experiments are consistent with historical CO₂ increases and (ii) the CO₂ increase influences plant sensitivity to water shortage, through either increased WUE or c_i in arid and wet environments, respectively.

A Proof of Concept Study to Detect Urease Producing Bacteria in Lungs Using Aerosolized 13C-Urea

This is a "proof of concept" study to determine whether inhalation of ¹³C-urea can be safely used to detect the presence of urease producing bacteria in the airways of patients with cystic fibrosis (CF) by detecting ¹³CO₂ in breath. This was a prospective, 2-part, open label, single-center, single-arm, single-administration, dose-escalation investigational device exemption trial. First, the safety of 20 and 50 mg inhaled ¹³C-urea was evaluated in 6 healthy adult participants. Then, 3 adult CF participants colonized with Pseudomonas aeruginosa were enrolled for each dose of inhaled ¹³C-urea. The safety of inhaled ¹³C-urea was assessed by spirometry and physical examination. ¹³C-urea was administered using a jet nebulizer, followed by serial spirometry (10 min and 30 min post inhalation) and collection of exhaled breath at 5, 10, and 15 min post inhalation. There was no clinical significant change in any of the spirometry values compared to baseline in healthy participants and CF patients. Mean of ¹³CO₂/¹²CO₂ delta over baseline (DOB) values in CF participants at 5, 10, and 15 min post inhalation was as follows: 20 mg dose 4‰ (2.2‰-4.9‰), 1‰ (1.0‰-1.4‰), and 1‰ (0.4‰-1.5‰); 50 mg dose: 10‰ (6.2‰-14.5‰), 3‰ (2.1‰-4.3‰), and 1.5‰ (0.6‰-2.3‰). Inhaled ¹³C-urea for detection of urease producing bacteria was safe, and preliminary data suggest that ¹³CO₂/¹²CO₂ DOB values may be higher in CF patients with P. aeruginosa at 5-10 min after inhalation of ¹³C-urea. A future direction is to investigate use of inhaled ¹³C-urea in young children who have difficulty producing sputum for culturing.

Spatiotemporal control of estrogen-responsive transcription in ERα-positive breast cancer cells

Recruitment of transcription machinery to target promoters for aberrant gene expression has been well studied, but underlying control directed by distant-acting enhancers remains unclear in cancer development. Our previous study demonstrated that distant estrogen response elements (DEREs) located on chromosome 20q13 are frequently amplified and translocated to other chromosomes in ERα-positive breast cancer cells. In this study, we used three-dimensional interphase fluorescence in situ hybridization to decipher spatiotemporal gathering of multiple DEREs in the nucleus. Upon estrogen stimulation, scattered 20q13 DEREs were mobilized to form regulatory depots for synchronized gene expression of target loci. A chromosome conformation capture assay coupled with chromatin immunoprecipitation further uncovered that ERα-bound regulatory depots are tethered to heterochromatin protein 1 (HP1) for coordinated chromatin movement and histone modifications of target loci, resulting in transcription repression. Neutralizing HP1 function dysregulated the formation of DERE-involved regulatory depots and transcription inactivation of candidate tumor-suppressor genes. Deletion of amplified DEREs using the CRISPR/Cas9 genomic-editing system profoundly altered transcriptional profiles of proliferation-associated signaling networks, resulting in reduction of cancer cell growth. These findings reveal a formerly uncharacterized feature wherein multiple copies of the amplicon congregate as transcriptional units in the nucleus for synchronous regulation of function-related loci in tumorigenesis. Disruption of their assembly can be a new strategy for treating breast cancers and other malignancies.

Divergent tissue and sex effects of rapamycin on the proteasome-chaperone network of old mice

Rapamycin, an allosteric inhibitor of the mTOR kinase, increases longevity in mice in a sex-specific manner. In contrast to the widely accepted theory that a loss of proteasome activity is detrimental to both life- and healthspan, biochemical studies in vitro reveal that rapamycin inhibits 20S proteasome peptidase activity. We tested if this unexpected finding is also evident after chronic rapamycin treatment in vivo by measuring peptidase activities for both the 26S and 20S proteasome in liver, fat, and brain tissues of old, male and female mice fed encapsulated chow containing 2.24 mg/kg (14 ppm) rapamycin for 6 months. Further we assessed if rapamycin altered expression of the chaperone proteins known to interact with the proteasome-mediated degradation system (PMDS), heat shock factor 1 (HSF1), and the levels of key mTOR pathway proteins. Rapamycin had little effect on liver proteasome activity in either gender, but increased proteasome activity in female brain lysates and lowered its activity in female fat tissue. Rapamycin-induced changes in molecular chaperone levels were also more substantial in tissues from female animals. Furthermore, mTOR pathway proteins showed more significant changes in female tissues compared to those from males. These data show collectively that there are divergent tissue and sex effects of rapamycin on the proteasome-chaperone network and that these may be linked to the disparate effects of rapamycin on males and females. Further our findings suggest that rapamycin induces indirect regulation of the PMDS/heat-shock response through its modulation of the mTOR pathway rather than via direct interactions between rapamycin and the proteasome.

Terrestrial water fluxes dominated by transpiration

Renewable fresh water over continents has input from precipitation and losses to the atmosphere through evaporation and transpiration. Global-scale estimates of transpiration from climate models are poorly constrained owing to large uncertainties in stomatal conductance and the lack of catchment-scale measurements required for model calibration, resulting in a range of predictions spanning 20 to 65 per cent of total terrestrial evapotranspiration (14,000 to 41,000 km(3) per year) (refs 1, 2, 3, 4, 5). Here we use the distinct isotope effects of transpiration and evaporation to show that transpiration is by far the largest water flux from Earth's continents, representing 80 to 90 per cent of terrestrial evapotranspiration. On the basis of our analysis of a global data set of large lakes and rivers, we conclude that transpiration recycles 62,000 ± 8,000 km(3) of water per year to the atmosphere, using half of all solar energy absorbed by land surfaces in the process. We also calculate CO2 uptake by terrestrial vegetation by connecting transpiration losses to carbon assimilation using water-use efficiency ratios of plants, and show the global gross primary productivity to be 129 ± 32 gigatonnes of carbon per year, which agrees, within the uncertainty, with previous estimates. The dominance of transpiration water fluxes in continental evapotranspiration suggests that, from the point of view of water resource forecasting, climate model development should prioritize improvements in simulations of biological fluxes rather than physical (evaporation) fluxes.

Hydrogen isotope correction for laser instrument measurement bias at low water vapor concentration using conventional isotope analyses: application to measurements from Mauna Loa Observatory, Hawaii

The hydrogen and oxygen isotope ratios of water vapor can be measured with commercially available laser spectroscopy analyzers in real time. Operation of the laser systems in relatively dry air is difficult because measurements are non-linear as a function of humidity at low water concentrations. Here we use field-based sampling coupled with traditional mass spectrometry techniques for assessing linearity and calibrating laser spectroscopy systems at low water vapor concentrations. Air samples are collected in an evacuated 2 L glass flask and the water is separated from the non-condensable gases cryogenically. Approximately 2 µL of water are reduced to H(2) gas and measured on an isotope ratio mass spectrometer. In a field experiment at the Mauna Loa Observatory (MLO), we ran Picarro and Los Gatos Research (LGR) laser analyzers for a period of 25 days in addition to periodic sample collection in evacuated flasks. When the two laser systems are corrected to the flask data, they are strongly coincident over the entire 25 days. The δ(2)H values were found to change by over 200‰ over 2.5 min as the boundary layer elevation changed relative to MLO. The δ(2)H values ranged from -106 to -332‰, and the δ(18)O values (uncorrected) ranged from -12 to -50‰. Raw data from laser analyzers in environments with low water vapor concentrations can be normalized to the international V-SMOW scale by calibration to the flask data measured conventionally. Bias correction is especially critical for the accurate determination of deuterium excess in dry air.

13[C]-urea breath test as a novel point-of-care biomarker for tuberculosis treatment and diagnosis

Background

Pathogen-specific metabolic pathways may be detected by breath tests based on introduction of stable isotopically-labeled substrates and detection of labeled products in exhaled breath using portable infrared spectrometers.

Methodology/Principal Findings

We tested whether mycobacterial urease activity could be utilized in such a breath test format as the basis of a novel biomarker and diagnostic for pulmonary TB. Sensitized New-Zealand White Rabbits underwent bronchoscopic infection with either Mycobacterium bovis or Mycobacterium tuberculosis. Rabbits were treated with 25 mg/kg of isoniazid (INH) approximately 2 months after infection when significant cavitary lung pathology was present. [¹³C] urea was instilled directly into the lungs of intubated rabbits at selected time points, exhaled air samples analyzed, and the kinetics of δ¹³CO₂ formation were determined. Samples obtained prior to inoculation served as control samples for background ¹³CO₂ conversion in the rabbit model. ¹³CO₂, from metabolic conversion of [¹³C]-urea by mycobacterial urease activity, was readily detectable in the exhaled breath of infected rabbits within 15 minutes of administration. Analyses showed a rapid increase in the rate of ¹³CO₂ formation both early in disease and prior to treatment with INH. Following INH treatment, all evaluable rabbits showed a decrease in the rate of ¹³CO₂ formation.

Conclusions/Significance

Urea breath testing may provide a useful diagnostic and biomarker assay for tuberculosis and for treatment response. Future work will test specificity for M. tuberculosis using lung-targeted dry powder inhalation formulations, combined with co-administering oral urease inhibitors together with a saturating oral dose of unlabeled urea, which would prevent the δ¹³CO₂ signal from urease-positive gastrointestinal organisms.

The chlorine isotope composition of the moon and implications for an anhydrous mantle

Arguably, the most striking geochemical distinction between Earth and the Moon has been the virtual lack of water (hydrogen) in the latter. This conclusion was recently challenged on the basis of geochemical data from lunar materials that suggest that the Moon's water content might be far higher than previously believed. We measured the chlorine isotope composition of Apollo basalts and glasses and found that the range of isotopic values [from -1 to +24 per mil (per thousand) versus standard mean ocean chloride] is 25 times the range for Earth. The huge isotopic spread is explained by volatilization of metal halides during basalt eruption--a process that could only occur if the Moon had hydrogen concentrations lower than those of Earth by a factor of approximately 10(4) to 10(5), implying that the lunar interior is essentially anhydrous.

Design of aging intervention studies: the NIA interventions testing program

The field of biogerontology has made great strides towards understanding the biological processes underlying aging, and the time is ripe to look towards applying this knowledge to the pursuit of aging interventions. Identification of safe, inexpensive, and non-invasive interventions that slow the aging process and promote healthy aging could have a significant impact on quality of life and health care expenditures for the aged. While there is a plethora of supplements and interventions on the market that purport to slow aging, the evidence to validate such claims is generally lacking. Here we describe the development of an aging interventions testing program funded by the National Institute on Aging (NIA) to test candidate interventions in a model system. The development of this program highlights the challenges of long-term intervention studies and provides approaches to cope with the stringent requirements of a multi-site testing program.

A field and laboratory method for monitoring the concentration and isotopic composition of soil CO2

The stable isotope composition of nmol size gas samples can be determined accurately and precisely using continuous flow isotope ratio mass spectrometry (IRMS). We have developed a technique that exploits this capability in order to measure delta13C and delta18O values and, simultaneously, the concentration of CO2 in sub-mL volume soil air samples. A sampling strategy designed for monitoring CO2 profiles at particular locations of interest is also described. This combined field and laboratory technique provides several advantages over those previously reported: (1) the small sample size required allows soil air to be sampled at a high spatial resolution, (2) the field setup minimizes sampling times and does not require powered equipment, (3) the analytical method avoids the introduction of air (including O2) into the mass spectrometer thereby extending filament life, and (4) pCO2, delta13C and delta18O are determined simultaneously. The reproducibility of measurements of CO2 in synthetic tank air using this technique is: +/-0.08 per thousand (delta13C), +/-0.10 per thousand (delta18O), and +/-0.7% (pCO2) at 5550 ppm. The reproducibility for CO2 in soil air is estimated as: +/-0.06 per thousand (delta13C), +/-0.06 per thousand (delta18O), and +/-1.6% (pCO2). Monitoring soil CO2 using this technique is applicable to studies concerning soil respiration and ecosystem gas exchange, the effect of elevated atmospheric CO2 (e.g. free air carbon dioxide enrichment) on soil processes, soil water budgets including partitioning evaporation from transpiration, pedogenesis and weathering, diffuse solid-earth degassing, and the calibration of speleothem and pedogenic carbonate delta13C values as paleoenvironmental proxies.

Chlorine isotope homogeneity of the mantle, crust and carbonaceous chondrites

Chlorine in the Earth is highly depleted relative to carbonaceous chondrites and solar abundances. Knowledge of the Cl concentrations and distribution on Earth is essential for understanding the origin of these depletions. Large differences in the stable chlorine isotope ratios of meteoritic, mantle and crustal materials have been used as evidence for distinct reservoirs in the solar nebula and to calculate the relative proportions of Cl in the mantle and crust. Here we report that large isotopic differences do not exist, and that carbonaceous chondrites, mantle and crust all have the same 37Cl/35Cl ratios. We have further analysed crustal sediments from the early Archaean era to the Recent epoch and find no systematic isotopic variations with age, demonstrating that the mantle and crust have always had the same delta37Cl value. The similarity of mantle, crust and carbonaceous chondrites establishes that there were no nebular reservoirs with distinct isotopic compositions, no isotopic fractionation during differentiation of the Earth and no late (post-core formation) Cl-bearing volatile additions to the crustal veneer with a unique isotopic composition.

Subduction and recycling of nitrogen along the Central American margin

We report N and He isotopic and relative abundance characteristics of volatiles emitted from two segments of the Central American volcanic arc. In Guatemala, delta15N values are positive (i.e., greater than air) and N2/He ratios are high (up to 25,000). In contrast, Costa Rican N2/He ratios are low (maximum 1483) and delta15N values are negative (minimum -3.0 per mil). The results identify shallow hemipelagic sediments, subducted into the Guatemalan mantle, as the transport medium for the heavy N. Mass balance arguments indicate that the subducted N is efficiently cycled to the atmosphere by arc volcanism. Therefore, the subduction zone acts as a "barrier" to input of sedimentary N to the deeper mantle.

Subnuclear dynamics and transcription factor function

At a simplistic level, the nucleus can be thought of as singular organelle with a nuclear envelope designed to isolate the biochemical reactions required for gene transcription and DNA replication from the cytoplasm. It has become increasingly clear, however, that many higher levels of organization exist within the nucleus. A functional consequence of this organization is that nuclear processes that include transcription, RNA processing, and DNA synthesis are isolated to specific intranuclear domains to ensure efficiency. With the advent of GFP technologies and increasingly sophisticated instrumentation, we have continued to dissect the relationship between organization and function, in particular using live cells and ligand-dependent steroid receptors as a model system. These new opportunities have provided further insight into receptor function and the dependence upon intranuclear dynamics that take place within minutes of hormone addition. J. Cell. Biochem. Suppl. 35:99-106, 2000.

Chuar Group of the Grand Canyon: record of breakup of Rodinia, associated change in the global carbon cycle, and ecosystem expansion by 740 Ma

The Chuar Group (approximately 1600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at low latitudes during extension on the north-trending Butte fault system and is inferred to record rifting during the breakup of Rodinia. Shallow-marine deposition is documented by tide- and wave-generated sedimentary structures, facies associations, and fossils. C isotopes in organic carbon show large stratigraphic variations, apparently recording incipient stages of the marked C isotopic fluctuations that characterize later Neoproterozoic time. Upper Chuar rocks preserve a rich biota that includes not only cyanobacteria and algae, but also heterotrophic protists that document increased food web complexity in Neoproterozoic ecosystems. The Chuar Group thus provides a well-dated, high-resolution record of early events in the sequence of linked tectonic, biogeochemical, environmental, and biological changes that collectively ushered in the Phanerozoic Eon.

Expression of BRC repeats in breast cancer cells disrupts the BRCA2-Rad51 complex and leads to radiation hypersensitivity and loss of G(2)/M checkpoint control

BRCA2 is a breast tumor suppressor with a potential function in the cellular response to DNA damage. BRCA2 binds to Rad51 through its BRC repeats. In support of the biological significance of this interaction, we found that the complex of BRCA2 and Rad51 in breast cancer MCF-7 cells was diminished upon conditional expression of a wild-type, but not a mutated, BRC4 repeat using the tetracycline-inducible system. Cells expressing a wild-type BRC4 repeat showed hypersensitivity to gamma-irradiation, an inability to form Rad51 radiation-induced foci, and a failure of radiation-induced G(2)/M, but not G(1)/S, checkpoint control. These results strongly suggest that the interaction between BRCA2 and Rad51 mediated by BRC repeats is critical for the cellular response to DNA damage.

Association of BRCA1 with the hRad50-hMre11-p95 complex and the DNA damage response

BRCA1 encodes a tumor suppressor that is mutated in familial breast and ovarian cancers. Here, it is shown that BRCA1 interacts in vitro and in vivo with hRad50, which forms a complex with hMre11 and p95/nibrin. Upon irradiation, BRCA1 was detected in discrete foci in the nucleus, which colocalize with hRad50. Formation of irradiation-induced foci positive for BRCA1, hRad50, hMre11, or p95 was dramatically reduced in HCC/1937 breast cancer cells carrying a homozygous mutation in BRCA1 but was restored by transfection of wild-type BRCA1. Ectopic expression of wild-type, but not mutated, BRCA1 in these cells rendered them less sensitive to the DNA damage agent, methyl methanesulfonate. These data suggest that BRCA1 is important for the cellular responses to DNA damage that are mediated by the hRad50-hMre11-p95 complex.

Binding of CtIP to the BRCT repeats of BRCA1 involved in the transcription regulation of p21 is disrupted upon DNA damage

Mutations in BRCA1 are responsible for nearly all of the hereditary ovarian and breast cancers, and about half of those in breast cancer-only kindreds. The ability of BRCA1 to transactivate the p21 promoter can be inactivated by mutation of the conserved BRCA1 C-terminal (BRCT) repeats. To explore the mechanisms of this BRCA1 function, the BRCT repeats were used as bait in a yeast two-hybrid screen. A known protein, CtIP, a co-repressor with CtBP, was found. CtIP interacts specifically with the BRCT repeats of BRCA1, both in vitro and in vivo, and tumor-derived mutations in this region abolished these interactions. The association of BRCA1 with CtIP was also abrogated in cells treated with DNA-damaging agents including UV, gamma-irradiation, and adriamycin, a response correlated with BRCA1 phosphorylation. The transactivation of the p21 promoter by BRCA1 was diminished by expression of exogenous CtIP and CtBP. These results suggest that the binding of the BRCT repeats of BRCA1 to CtIP/CtBP is critical in mediating transcriptional regulation of p21 in response to DNA damage.

Thyroid hormone, T3-dependent phosphorylation and translocation of Trip230 from the Golgi complex to the nucleus

Trip230 is a novel coactivator of the thyroid hormone receptor that is negatively regulated by the retinoblastoma tumor-suppressor protein. In an examination of its subcellular distribution, Trip230 localized predominantly to the vicinity of the Golgi instead of the nucleus, as other nuclear hormone receptor coactivators. Using a series of deletion mutants, a critical region identified for Golgi area targeting coincided with a previously defined thyroid hormone receptor-binding domain of Trip230. During cell cycle progression, the expression level of Trip230 is constant and a significant portion is imported into the nucleus at S phase. Within an hour of treating cells with T3, Trip230 immunofluorescence transiently colocalized with TR in prominent subnuclear structures. T3-dependent nuclear import of Trip230 does not require new protein synthesis. Coincident with T3 treatment and nuclear import, newly phosphorylated residue(s) appeared in Trip230, suggesting that phosphorylation may be involved in its nuclear import. These findings provided a novel mechanism for the regulation of nuclear hormone transcription factors by hormone-responsive phosphorylation and nuclear import of cytoplasmically located coactivators.

Subnuclear partitioning and functional regulation of the Pit-1 transcription factor

Subnuclear compartmentation is postulated to play an important role in many aspects of nuclear metabolism. To directly test an application of this model to transcription factor function, we examined the subnuclear partitioning behavior of Pit-1, a tissue-specific, POU-class transactivator. Biochemical and in situ assays indicate the nuclear pool of Pit-1 is normally divided between two compartments: the majority being differentially soluble in detergent, and a significant insoluble fraction (approximately 20%) bound to the nuclear matrix. Examination of Pit-1 deletion mutants and chimeric fusions reveal the highly conserved 66 amino acid POU-specific domain contains a necessary and sufficient nuclear matrix targeting signal. The nuclear partitioning behavior of several natural or engineered point mutations of Pit-1 was also examined. Surprisingly, the inactive point mutants were completely matrix-bound, irrespective of their ability to bind Pit-1 specific DNA. These results suggest that dynamic partitioning of Pit-1 is a component of its normal transactivator function that takes place upon the insoluble nuclear substructure where transcription occurs.

Application of exogenously regulatable promoter systems to transgenic models for the study of aging

Transgenic mouse and gene knockout technologies offer powerful tools for dissecting the roles of specific genes in the process of aging. Tke interpretation of the results of such studies is limited, however, by the fact that the gene of interest of over- or underexpressed throughout the life span of the animal model. Among other problems, this situation makes it difficult to separate the effects that a specific gene has an embryological development from those that it may exert on the subsequent maturation and aging of the animal. It is also not possible with these methods alone to alter the expression of genes in an age-dependent fashion and to assess the effects of these alterations on the aging process. This capacity would be of particular interest in studying genes which are thought to have a role in regulating physiological homeostasis. Because they offer the opportunity to activate or render inactive the expression of genes at will, exogenously regulatable promoter systems, particularly when used in combination with traditional transgenic or gene knockout approaches, provide a new and potentially very powerful tool for studying the effect of selected genes on aging. This review discusses the merits and limitations of the application of either the tetracycline-regulatable promoter system, the RU 486-inducible promoter system, or the ecdysone-inducible promoter system to exogenously regulate the expression of a transcriptionally linked gene and to thus assess the effect of that gene on aging.

Functional subnuclear partitioning of transcription factors

After many years of reductionistic approaches to characterize molecular mechanisms involved in transcription, the number of factors recognized to take part in this process has increased remarkably and continues to grow. When considering posttranslational modifications in conjunction with the large number of factors involved in modulating the activity of transcription complex components, the overall intricacy becomes staggering. After two decades of intensive molecular investigations, there has been a concerted effort to integrate these findings with cellular approaches to understand transcription on a more global level. This sort of reasoning actually revisits studies of approximately 20 years ago that considered the functional consequences of steroid receptor association with nuclear structure. With an abundance of new molecular probes and increasingly powerful instruments to detect them in fixed and, more recently, live cells, the issue of functional subnuclear organization is receiving increased attention. In this report, we focus on advances in characterizing the functional significance of transcription factor association with the nucleoskeleton. In particular, we consider recent biochemical and "molecular morphology" data that point to the importance of dynamic spatial and solubility partitioning of gene regulators with nuclear architecture.

The BRC repeats in BRCA2 are critical for RAD51 binding and resistance to methyl methanesulfonate treatment

The BRCA2 gene was identified based on its involvement in familial breast cancer. The analysis of its sequence predicts that the gene encodes a protein with 3,418 amino acids but provides very few clues pointing to its biological function. In an attempt to address this question, specific antibodies were prepared that identified the gene product of BRCA2 as a 390-kDa nuclear protein. Furthermore, direct binding of human RAD51 to each of the four single 30-amino acid BRC repeats located at the 5' portion of exon 11 of BRCA2 was demonstrated. Such an interaction is significant, as BRCA2 and RAD51 can be reciprocally coimmunoprecipitated by each of the individual, specific antibodies and form complexes in vivo. Inferring from the function of RAD51 in DNA repair, human pancreatic cancer cells, Capan-1, expressing truncated BRCA2 were shown to be hypersensitive to methyl methanesulfonate (MMS) treatment. Exogenous expression of wild-type BRCA2, but not BRC-deleted mutants, in Capan-1 cells confers resistance to MMS treatment. These results suggest that the interaction between the BRC repeats of BRCA2 and RAD51 is critical for cellular response to DNA damage caused by MMS.

HEC binds to the seventh regulatory subunit of the 26 S proteasome and modulates the proteolysis of mitotic cyclins

A newly identified nuclear protein rich in leucine heptad repeats called HEC is important for mitosis. To elucidate its mechanism of action, the region containing leucine heptad repeats was used to identify cellular proteins that potentially interact with HEC. Complementary DNAs encoding several proteins including MSS1, p45, Nek2, and Smc1/Smc2, known to be important for G2/M progression, were identified. The interaction between HEC and MSS1, the seventh regulatory subunit of the 26 S proteasome, was further demonstrated by in vitro GST pull-down assays. HEC is not a part of the 26 S proteasome and interacts with MSS1 only when it is dissociated from the complex during M phase. Purified MSS1 specifically hydrolyzes ATP, an activity inhibited by HEC. In addition, HEC inhibits the proteolysis of mitotic cyclin B in vitro. Consistent with this biochemical activity, ectopic expression of HEC inhibits the degradation of mitotic cyclins after telophase, resulting eventually in cell death. These results show that HEC is a negative regulator of MSS1 and suggest that it may modulate M phase progression, in part, through the regulation of proteasome-mediated degradation of cell cycle regulatory proteins.

The nuclear localization sequences of the BRCA1 protein interact with the importin-alpha subunit of the nuclear transport signal receptor

The BRCA1 gene product is a nuclear phosphoprotein that is aberrantly localized in the cytoplasm of most breast cancer cells. In an attempt to elucidate the potential mechanism for the nuclear transport of BRCA1 protein, three regions of highly charged, basic residues, 503KRKRRP508, 606PKKNRLRRKS615, and 651KKKKYN656, were identified as potential nuclear localization signals (NLSs). These three regions were subsequently mutated to 503KLP508, 607KLS615, and 651KLN656, respectively. Wild-type and mutated proteins were tagged with the flag epitope, expressed in human DU145 cells, and detected with the M2 monoclonal antibody. In DU145 cells, the KLP mutant completely fails to localize in nuclei, whereas the KLS mutant is mostly cytoplasmic with occasional nuclear localization. The KLN protein is always located in nuclei. Consistently, hSRP1alpha (importin-alpha), a component of the NLS receptor complex, was identified in a yeast two-hybrid screen using BRCA1 as the bait. The specificity of the interaction between BRCA1 and importin-alpha was further demonstrated by showing that the 503KRKRRP508 and 606PKKNRLRRKS615 regions, but not 651KKKKYN656, are critical for this interaction. To determine if the cytoplasmic mislocation of endogenous BRCA1 in breast cancer cells is due to a deficiency of the cells, wild-type BRCA1 protein tagged with the flag epitope was ectopically expressed in six breast cancer cell lines. The analysis demonstrated that, in all six, this protein localized in the cytoplasm of these cells. In contrast, expression of the construct in four non-breast cancer cell lines resulted in nuclear localization. These data support the possibility that the mislocation of the BRCA1 protein in breast cancer cells may be due to a defect in the cellular machinery involved in the NLS receptor-mediated pathway of nuclear import.

Brain POU-er

Developmental coordination is vital in the temporally coordinated appearance of cell types within the precise spatial architecture of the vertebrate brain and this, combined with the rich interplay between the developing brain and its target organs, is a biological problem of monumental complexity. An example is the genesis and subsequent integration of the neuroendocrine hypothalamus and the pituitary. Two recent papers use the developing hypothalamo-pituitary axis in order to gather a deeper understanding of these integrative mechanisms. In addition, they show that a sub-family of homeodomain factors, the POU-domain proteins, play a critical role in coordinating the respective ontogenies of the hypothalamus and the pituitary.

3.6 kb of the 5' flanking DNA activates the mouse tyrosine hydroxylase gene promoter without catecholaminergic-specific expression

The tyrosine hydroxylase (TH) gene is expressed exclusively in cells and neurons that synthesize and release L-DOPA or catecholamines. To further understand the molecular genetic mechanisms that regulate this cell-type specific expression, a chimeric gene was prepared by linking 3.6 kb of the 5' flanking DNA of the mouse TH gene, including the +1 initiation site for transcription, to an E. coli beta-galactosidase reporter. This fusion gene (TH3.6LAC) was used to prepare transgenic mice, and the tissue distribution of expression of TH3.6LAC was determined by the measurement of beta-galactosidase enzymatic activity and/or by the detection of the transcription product of the chimeric gene by RNase protection assays. In two separate founder lines, TH3.6LAC expression was observed in every region of the brain that was examined, including the olfactory bulb, brainstem, cerebellum, diencephalon, hippocampus, striatum, and cerebral cortex. Expression of TH3.6LAC was observed in the adrenal gland of one founder line but not in the other. TH3.6LAC activation was undetectable in peripheral organs that were examined, including the liver, heart, salivary gland, kidney, lung, and spleen. Although 3.6 kb of the 5' regulatory DNA of the mouse TH gene is sufficient to activate the TH fusion gene in the mouse, it is not enough to restrict its expression to catecholaminergic cells.

Pit-1 exhibits a unique promoter spacing requirement for activation and synergism

The developmentally regulated Pit-1 transcription factor is involved in the activation of prolactin, growth hormone, and TSH beta expression. Using templates with spacing mutations to program an in vitro transcription system, the activity of a single Pit-1 proximal binding site within the rat prolactin promoter was shown to have a unique bimodal distance requirement. Transcription activity rapidly decreased with each 5-base pair (bp) addition to the spacing between the binding site and the TATA box. When positioned 20 bp upstream from its normal -36 position in the prolactin promoter, the activity of the Pit-1 binding site is reduced to basal levels. Placement of the site at a position 30 bp upstream resulted in a return of Pit-1-mediated activation. Using transient transfection assays in GH3 cells, the prime bimodal sites are also a requirement for optimum expression of chimeric prolactin-luciferase reporter constructs. Interestingly, optimal synergism of transcription in vivo by the prolactin distal enhancer, containing four Pit-1 binding sites and an estrogen-responsive element, is also sensitive to the placement of the proximal Pit-1 binding site. These data have important implications for Pit-1 activator function in pituitary cells and for general models of transcription synergism.

Rat Pit-1 stimulates transcription in vitro by influencing pre-initiation complex assembly

The anterior pituitary-specific transcription factor, Pit-1, activates prolactin, growth hormone, TSH beta, growth hormone receptor genes and autoregulates the pit-1 gene. Its mechanism of transcription activation is unknown. Using immobilized DNA templates and order-of-addition transcription assays, it is shown that Pit-1 is required during pre-initiation complex assembly to activate the prolactin gene in vitro. Using prolactin promoters containing point mutations in the distal TATA box, it is also demonstrated that Pit-1 activation in vitro is not mediated simply by repressing the upstream, alternative promoter. Experiments show that a preformed class II pre-initiation complex is refractory to Pit-1 influence. The data indicate that Pit-1, and perhaps other members of the POU-protein family, activate transcription by influencing the type pre-initiation complex assembled on target promoters.

A Pit-1 binding site 3' to the transcription start site inhibits transcription elongation in vitro

The transcription factor Pit-1 can autoregulate its own expression by interacting with binding sites associated with the Pit-1 gene. One of these binding sites is located within the transcribed region of the gene and appears to be responsible for negatively regulating Pit-1 transcription. Using unique constructions in an in vitro transcription system, we show here that binding of Pit-1 to its recognition element can impede the progress of transcription elongation through the occupied site. We propose that this is a viable mechanism for Pit-1 autoregulation.

Cloning of the nucleic acid-binding domain of the rat HnRNP C-type protein

A cDNA encoding the nucleic acid-binding domain of the hnRNP C-type protein has been cloned by DNA-affinity screening of pituitary-derived expression libraries. An analysis revealed sequence identity with the human C-type cDNA and demonstrated the presence of a peptide sequence contained within the single-stranded DNA-binding protein, UP2, which was absent from the human cDNA. Structural analysis of the protein encoded by the rat cDNA demonstrated a net charge of +15 with 14.56% and 6.33% lysines and arginines, respectively, and an amino acid sequence that is consistent with an extensive helix-loop-helix-turn-helix structure.

Regulation of cell-type-specific transcription and differentiation of the pituitary

The transcription of rat prolactin and growth hormone genes in vitro requires a pituitary transcription factor, specific to certain cell types in the pituitary, which currently appears to be the PUF-I/Pit-1/GHF-1 protein. This factor binds to cis-regulatory elements in the 5' region of both genes and exerts a positive influence on transcription initiation presumably by interacting with general transcription factors. The PUF-I/Pit-1/GHF-1 transcriptional regulatory protein probably has an important role in not only the differentiation of the pituitary lactotroph/somatotroph cell lineage; it is also expressed in the early development of the nervous system but its function there is less well documented. It appears to be one member of a family of trans-activator proteins involved in differential gene expression in several cell types.

Proto-oncogene analyses in brain tumors

The present study determined which oncogenes (N-myc, c-myc, v-sis, or v-fos) were amplified and which messenger ribonucleic acids (mRNA's) accumulated in 10 primary human brain tumors of neuroectodermal origin. The tumors included four glioblastomas multiforme, one mixed glioma (astrocytoma grade I and ependymoma), one astrocytoma grade II, one cystic cerebellar astrocytoma, one ependymoma, one ganglioglioma, and one medulloblastoma. The relative amounts of polyadenylated (poly(A)+) RNA's homologous to these genes and their copy number were determined using the RNA and deoxyribonucleic acid blot hybridization techniques. The N-myc and v-sis probes hybridized strongly to the poly(A)+ RNA from the same recurrent glioblastoma with gene amplifications (N-myc 80 copies; v-sis three to four copies). The c-myc probe hybridized strongly to the recurrent medulloblastoma without gene amplification. The amplification or abundant accumulation of mRNA's homologous to their oncogenes may be involved in tumorigenesis or the aggressiveness of these malignant brain tumors of neuroectodermal origin and may be good molecular indicators of an extremely malignant state in these tumors.

DNA recognition element required for PUF-I mediated cell-type-specific transcription of the rat prolactin gene

The cell-type-specific transcription of the prolactin gene in vitro is mediated through the interaction of prolactin upstream factor I (PUF-I) with a 28 basepair region of the gene promoter (-63 to -36) which contains an 18 bp A+T-rich imperfect palindrome (-63 to -46). Base substitutions were introduced into 16 of the 18 palindromic residues by targeted saturation mutagenesis. The GH3 binding and in vitro transcription assays of the mutated promoters showed that base substitutions within the 5'-ATATTCA-3' sequence located at -52 to -46 were detrimental to PUF-I binding and its cell-type-specific transcriptional enhancement activity. Transcription assays of the mutated promoters performed with several nonpituitary-derived extracts demonstrated that a distal TATA box located from -59 to -53 promotes initiation at -27. Thus, the cell-type-specific cis-acting element required by PUF-I for DNA recognition is immediately adjacent to a general TATA sequence. Base substitutions that decreased +1 transcription and PUF-I binding concomitantly increased -27 initiation of RNA in vitro. We suggest that PUF-I binding in pituitary cells potentiates +1 transcription and represses alternative TATA box activity for initiation events occurring at -27. This is the first known report of a eukaryotic DNA binding protein that has both an activator and repressor activity for a single transcription unit.

Dual functions of a cis-acting element within the rat prolactin gene promoter

Within the promoter region of the rat prolactin gene lies a TA-rich imperfect palindrome. The possible functions of the 18-base-pair symmetrical sequence were investigated by using an in vitro transcription system. Prolactin templates with and without the palindrome were transcriptionally assayed in both pituitary and nonpituitary extracts. Our results indicated that the palindromic sequence has at least two functions in the regulation of prolactin transcription.

Prolactin upstream factor I mediates cell-specific transcription

DNA sequence-specific chromatography was used to purify prolactin upstream factor I (PUF-I) approximately 10,000- to 20,000-fold from rat GH3 cells. The purified transcription factor reconstituted enhanced pituitary-specific prolactin RNA synthesis in nonpituitary in vitro transcription assays. In vitro mutagenesis demonstrated that the capacity to stimulate prolactin gene transcription was directly correlated with PUF-I binding to an A+T-rich region located from -63 to -36 in the prolactin 5'-flanking DNA. We propose that PUF-I is a critical modulator of transcriptional activity in pituitary cells and has a central role in the stimulation of prolactin gene transcription in the mammalian pituitary lactotroph.

Impaired proliferation response after PDGF induction in fibroblasts from Hutchinson-Guilford Progeria syndrome

Fibroblasts from a Hutchinson-Guilford Progeria Syndrome (HGPS) patient were compared to normal human fibroblasts to determine if differences existed in growth factor mediated cell proliferation. Cultures of progeric fibroblasts were exposed individually to platelet-derived growth factor (PDGF), epidermal growth factor (EGF), platelet poor plasma (PPP) and fetal bovine serum (FBS). Autoradiographic studies using 3H thymidine showed that progeric fibroblasts had similar labeling indices relative to controls after exposure to FBS and EGF. In contrast, progeric cells made competent with PDGF and later treated with 5% PPP had a significantly lower labeling index. This and preliminary observations on fos RNA accumulation suggests the possible existence of a genetic defect in HGPS fibroblasts.

Expression of three viral oncogenes (v-sis, v-myc, v-fos) in primary human brain tumors of neuroectodermal origin

We determined which viral oncogenes (v-sis, v-myc, and v-fos) were expressed in five primary human brain tumors of neuroectodermal origin (two glioblastomas multiforme, one medulloblastoma, one cystic cerebellar astrocytoma, and one ganglioglioma) and which of these oncogenes is correlated with malignancy. Using the dot hybridization technique, we determined the relative amounts of mRNA coded by these genes using the same nitrocellulose filter. The v-myc probe showed a 4- to 12-fold greater hybridization to the mRNA from two glioblastomas and the medulloblastoma (malignant group) than the mRNA from the cystic cerebellar astrocytoma or the ganglioglioma (benign group). In contrast, RNA hybridizing to v-sis and v-fos were accumulated to a greater extent in the benign tumors. These data suggest that the amount of myc expression may be correlated with the degree of malignancy of brain tumors of neuroectodermal origin.

Correlation of rat pituitary prolactin messenger ribonucleic acid and hormone content with serum levels during the estrogen-induced surge

The model of the serum PRL surge generated in the ovariectomized rat after estradiol benzoate (EB) treatment was used to study the relationship between serum and pituitary PRL levels and pituitary PRL mRNA levels. Adult ovariectomized rats were injected sc with 7 micrograms EB or vehicle at noon on day 0. Three days later (day 3), the rats were decapitated every 4 h over a 24-h period (0800 h on day 3 to 0400 h on day 4) for determination of serum and pituitary PRL and GH levels by RIA. In addition, PRL and GH mRNA content was determined using dot blot hybridization with cDNAs. Administration of EB resulted in a significant rise in serum PRL levels at 1200, 1600, and 2000 h on day 3 compared to control values. At other times, serum PRL levels in the EB group were the same as control values. EB treatment also elicited a marked increase in pituitary PRL content at all time periods examined except during (1600 and 2000 h) and after the PRL surge (2400 h on day 3) when there was a significant reduction in stored pituitary PRL. The pituitary PRL mRNA content in the EB-treated group was significantly elevated (4- to 6-fold) over control levels throughout the study. Furthermore, PRL mRNA levels in EB-treated rats were significantly higher at 2000 and 2400 h on day 3 than at other time periods. In contrast to its effects on PRL, EB treatment had a slight inhibitory effect on pituitary GH content at 2000 and 2400 h on day 3 compared to control values; otherwise, this steroid had no effect on serum GH levels and pituitary GH mRNA content. Interestingly, serum GH levels and pituitary GH mRNA content in both treatment and control groups fluctuated in a pattern consistent with circadian rhythms, with peak values occurring during the lights-on hours. These data show that estrogen has a stimulatory effect on pituitary content of PRL and its corresponding mRNA in the rat 3 days after injection. These elevated PRL mRNa levels may be necessary for the occurrence of PRL surges. Furthermore, the facts that serum PRL levels were elevated only at certain times (1200-2000 h on day 3) while PRL mRNA content was increased at all times in the EB-treated rats suggest a differential regulation between PRL release and biosynthesis.

Reconstitution of cell-type-specific transcription of the rat prolactin gene in vitro

We present evidence for the existence of prolactin upstream factor 1 (PUF-1) in rat pituitary-derived cells and demonstrate its interaction with a symmetrical DNA element located in the 5' flanking region of the gene. An in vitro expression system developed from pituitary-derived GH3 cells was used to determine that 420 base pairs (bp) of 5' flanking DNA was sufficient for cell-specific, accurate, and efficient RNA polymerase II transcription of the rat prolactin gene. Reconstitution of in vitro transcription with pituitary and nonpituitary nuclear extracts suggested that the presence of GH3 cell-specific factors mediated the activation of prolactin gene expression. We also demonstrated that a functionally stable transcription complex assembled on the prolactin promoter. Using DNase I protection procedures, we have identified the DNA-protein binding area in the prolactin 5' flanking region. GH3 nuclear extracts contain a cell-specific protein (PUF-I) that binds to a 28-bp region (-63 to -36)which contains an 18-bp imperfect palindrome (-63 to -46). The role that the interaction between PUF-I and the imperfect palindrome plays in in vitro pituitary-specific prolactin gene expression is discussed.

The ribosomal DNA transcription unit of the house cricket, Acheta domesticus

A composite map representing a single ribosomal DNA repeat unit of the house cricket, Acheta domesticus, was constructed from overlapping cloned fragments. Sites in the repeat unit for nine restriction enzymes were mapped. R-loop mapping of sequences coding for 18 S and 28 S RNA demonstrates that the 58-kb ribosomal DNA repeat unit contains a novel-sized internal transcribed spacer of 8.4 kb. The existence of this large spacer was confirmed in genomic DNA, most if not all of the genomic repeat units containing such a spacer. A 15- to 17-kb ribosomal RNA precursor transcript is synthesized as predicted on the basis of the size of the internal transcribed spacer. The 5.8 S RNA gene is localized to a 1-kb sequence immediately 5' to the 28 S gene. The coding regions examined contain no intervening sequences analogous to those described within ribosomal DNA of other eukaryotes. Only 11% of the repeat unit codes for mature ribosomal RNA, while the remainder is nontranscribed (71%) and transcribed (18%) spacer DNA.