Tobacco proliferating cell nuclear antigen binds directly and stimulates both activity and processivity of ddNTP-sensitive mungbean DNA polymerase

Immunohistochemical and biochemical alterations following administration of proanthocyanidin extract in rats hepatocellular carcinoma

Grape seed proanthocyanidin extract (GSPE) is known to be effective on broad spectrum of biological pathways in living organisms including oxidative stress. The present study aimed to investigate the effects of proanthocyanidin on preneoplastic lesions and liver cancer induced in rats by Diethylnitrosamine (DEN). 7-8 Week old male Sprague Dawley (S.D.) rats were divided into six groups: The 1st group received no treatment and were -ve controls, the 2nd were treated with a single dose of DEN 200mg/kg intraperitoneally (i.p.) and served as +ve control group. The 3rd and 4th groups were injected with the same dose of DEN as in group 2 and then post treated with 300 or 150mg/kg/b.wt./day GSPE by intrgastroluminal gavage (i.g.) respectively until the end after the 22 weeks. Groups 5 and 6 were treated with the same doses of GSPE as in groups 3 and 4 respectively without DEN administration. The results showed that the immunohistochemical Proliferating Cell Nuclear Antigen (PCNA) labeling indexes (PCNA LI%) were significantly inhibited in liver tissues and tumors by both treatments of GSPE. Furthermore, treatment with GSPE has modified the liver tissue oxidative stress markers levels of SOD, CAT, GSH, GST, GPx, GR and MDA changed by DEN. In conclusion, GSPE has a sufficient therapeutic effect against liver carcinogenesis through their free radical scavenging, inhibition of cellular proliferation.

The tomato DDI2, a PCNA ortholog, associating with DDB1-CUL4 complex is required for UV-damaged DNA repair and plant tolerance to UV stress

CULLIN 4 (CUL4)-DAMAGED DNA binding protein 1 (DDB1)-based ubiquitin E3 ligase modulates diverse cellular processes including repair of damaged genomic DNA. In this study, an uncharacterized gene termed as DDB1-Interacting protein 2 (DDI2) was identified in yeast two-hybrid screening with bait gene DDB1. The co-immunoprecipitation (co-IP) assays further demonstrated that DDI2 is associated with tomato DDB1-CUL4 complex in vivo. It appears that DDI2 encodes an ortholog of proliferating cell nuclear antigen (PCNA). Confocal microscope observation indicated that DDI2-GFP fusion protein was localized in nuclei. The expression of DDI2 gene is constitutive but substantially enhanced by UV-C irradiation. The transgenic tomato plants with overexpression or knockdown of DDI2 gene displayed the increased or decreased tolerance, respectively, to UV-C stress and chemical mutagen cisplatin. The quantitative analysis of UV-induced DNA lesions indicated that the dark repair of DNA damage was accelerated in DDI2 overexpression lines but delayed in knockdown lines. Conclusively, tomato DDI2 gene is required for UV-induced DNA damage repair and plant tolerance to UV stress. In addition, fruits of DDI2 transgenic plants are indistinguishable from that of wild type, regarding fresh weight and nutrient quality. Therefore, overexpression of DDI2 offers a suitable strategy for genetic manipulation of enhancing plant tolerance to UV stress.

Cell cycling with the SEB: a personal view

This review, written from a personal perspective, traces firstly the development of plant cell cycle research from the 1970s onwards, with some focus on the work of the author and of Dr Dennis Francis. Secondly there is a discussion of the support for and discussion of plant cell cycle research in the SEB, especially through the activities of the Cell Cycle Group within the Society's Cell Biology Section. In the main part of the review, selected aspects of DNA replication that have of been of special interest to the author are discussed. These are DNA polymerases and associated proteins, pre-replication events, regulation of enzymes and other proteins, nature and activation of DNA replication origins, and DNA endoreduplication. For all these topics, there is mention of the author's own work, followed by a brief synthesis of current understanding and a look to possible future developments.

Functional analysis of light-regulated promoter region of AtPolλ gene

Genetic and molecular analyses mainly in Arabidopsis and in some other plants have demonstrated involvement of light signaling in cell cycle regulation. In this report, we show light-mediated activation of the promoter of AtPolλ gene, a homolog of mammalian DNA polymerase λ in Arabidopsis thaliana and an important component of DNA damage repair/recombination machinery in plants. Analyses of the light-mediated promoter activity using various deletion versions of AtPolλ promoter in transformed Arabidopsis and tobacco (Nicotiana tabaccum) plants indicate that a 130-bp promoter region between -536 and -408 of AtPolλ promoter is essential for light-induced regulation of AtPolλ expression. DNA-protein interaction studies reveal that an ATCT-motif and AE-box light-responsive elements in the light-regulated promoter region confer light responsiveness of AtPolλ promoter. DNA-binding analysis has identified a 63-kDa trans-acting protein factor which showed specific binding to ATCT-motif, while another trans-acting factor of ~52 kDa was found to bind specifically to both ATCT and AE-box sequences. The 52-kDa protein has been identified as B3-domain transcription factor by MALDI-TOF/MS analysis. Overall, our results provide novel information on the role of light signaling in regulation of expression of an important component of DNA repair machinery in plants.

DNA repair and recombination in higher plants: insights from comparative genomics of Arabidopsis and rice

Background

The DNA repair and recombination (DRR) proteins protect organisms against genetic damage, caused by environmental agents and other genotoxic agents, by removal of DNA lesions or helping to abide them.

Results

We identified genes potentially involved in DRR mechanisms in Arabidopsis and rice using similarity searches and conserved domain analysis against proteins known to be involved in DRR in human, yeast and E. coli. As expected, many of DRR genes are very similar to those found in other eukaryotes. Beside these eukaryotes specific genes, several prokaryotes specific genes were also found to be well conserved in plants. In Arabidopsis, several functionally important DRR gene duplications are present, which do not occur in rice. Among DRR proteins, we found that proteins belonging to the nucleotide excision repair pathway were relatively more conserved than proteins needed for the other DRR pathways. Sub-cellular localization studies of DRR gene suggests that these proteins are mostly reside in nucleus while gene drain in between nucleus and cell organelles were also found in some cases.

Conclusions

The similarities and dissimilarities in between plants and other organisms' DRR pathways are discussed. The observed differences broaden our knowledge about DRR in the plants world, and raises the potential question of whether differentiated functions have evolved in some cases. These results, altogether, provide a useful framework for further experimental studies in these organisms.

An insight into the biological functions of family X-DNA polymerase in DNA replication and repair of plant genome

Recently we have reported the characterization of a novel single subunit 62-kDa polypeptide with ddNTP-sensitive DNA polymerase activity from the developing seeds of mungbean (Vigna radiata). The protein showed higher expression and activity level during nuclear endoreduplication stages of mungbean seeds and similarity with mammalian DNA polymerase beta in many physicochemical properties. The enzyme was found to specifically interact with PCNA (proliferating cell nuclear antigen), and expressed in both meristematic and meiotic tissues. Functional assays have demonstrated binding of the enzyme to normal and mismatched DNA substrates and with fidelity DNA synthesis in moderately processive mode, suggesting probable involvement of the enzyme in both replication and recombination. Here we have discussed the position of mungbean DNA polymerase as a homologue of DNA Pol lambda, one of the newly identified member of family-X DNA polymerase in plants and illustrated the functional relevance of this enzyme in maintaining the coordination between DNA replication and repair in plant genome.

Analysis of processivity of mungbean dideoxynucleotide-sensitive DNA polymerase and detection of the activity and expression of the enzyme in the meristematic and meiotic tissues and following DNA damaging agent

Analysis of the processivity of mungbean ddNTP-sensitive DNA polymerase showed the incorporation of approximately 35-40 nucleotides per binding event in the replication assays involving M13 ss DNA template with 5'-labeled 17-mer primer. Optimal processivity was obtained with 100-150 mM KCl and 6-8 mM Mg2+ at pH 7.5. The enzyme showed preference for Mg2+ over Mn2+ as the metal activator for processivity. 2', 3' dideoxythymidine 5' triphosphate (ddTTP) and rat DNA pol beta antibody strongly influenced distributive synthesis. Considerable enhancement in processivity was noticed at 1mM ATP and 2-4 mM spermidine while higher concentrations of spermidine caused distributive synthesis. The enzyme was found to be active in both meristematic and meiotic tissues and distinctly induced by EMS treatment. DNA-binding assays revealed distinct binding ability of the enzyme to template/primer and damaged DNA substrate. Together these observations illustrate the probable involvement of the enzyme in replication and repair machinery in higher plants.