although there are many repair pathways in cells, some lesions still escape repair inevitably and remain in genome. In cells, the molecular mechanism of translesion DNA synthesis has been one of the major unsolved problems in DNA repair for a long time. Recently, it was found that the members of a structurally related UmuC/DinB protein superfarnily have DNA polyrnerase function. Unlike the classical replicative DNA polymerases, these newly identified DNA polymerases can carry out translesion DNA synthesis in both error prone/mutagenic and/or error-free ways. It was also found that their functions are conserved from bacteria to human.

AIM: To find out common transcription factor binding sites in the promoter regions of the encoding genes of the co-expressive proteins induced by N-methyl-N'-nitro-N- nitrosoguanidine (MNNG). METHODS: Using phylogenetic footprinting and TRANSFAC position weight matrix (PWM) searching program to predict the common transcription factor binding sites among the promoter regions of the genes encoding the co-expressive proteins. The predictive results were validated with electrophoresis mobility shift assay (EMSA). RESULTS: Eleven common transcription factor binding sites were predicted in the promoters of the co-expressive proteins, among them, besides the activator protein 1(AP1) which was previously identified to be activated in MNNG pretreated cells in this laboratory, the nuclear factor Y (NFY) and GATA binding factor (GATA) consensus oligonucleotides binding activity were found being increased in the nuclear extract of cells pre-treated with MNNG as demonstrated by EMSA. CONCLUSION: Phylogenetic footprinting can effectively decrease the false positive rate in predicting transcription factor binding sites. It is possible that NFY and GATA transcription factor binding sites are involved in the co-regulation of the MNNG induced co- expressive proteins. [

A Review] A large quantity of intracellular structural and regulatory proteins can be covalently attached to ubiquitin posttranscriptionally and thus modified. The ubiquitination of proteins serves as targeting signals, making ubiquitinated proteins distributed to different parts of the cells, changing the activities, the interaction between macromolecules and the half-life of proteins. Therefore, ubiquitin conjugation is implicated in numerous metabolic processes in eukaryotes. Ubiquitin conjugates its protein substrates via a cascade reaction. This paper is a review of recent advances in this area.

Human genes typically contain multiple intron s, and in many cases the exons can be joined more than one way to generate multi ple mRNAs, encoding distinct protein isoforms. This process is called alternativ e splicing. The article summarized the human cytochrome P450 pre mRNA alternati v e splicing and their regulatory mechanism and impacts on biological functions.

Cytochrome P450 (CYP) is a complex gene superfamily of proteins that metabolizes a myriad of endogenous and exogenous substrates. Liver-enriched transcription factors (LETF) play a role in the constitutive and tissue-specific expression of hepatic genes. In this review, six families of LETF that play a role in the tissue-specific, developmental, sexual and temporal regulation of CYP are discussed.

AIM: To understand whether endoplasmic reticulum stress (ER-stress) is involved in DNA-damaging agent/carcinogen induced cell responses. METHODS: Three DNA-damaging agents/carcinogens different in the mode of action, ie, alkylating agent N-methyl-N’-nitro-N-nitrosoguanidine (MNNG), bulky adduct forming agent benzo[a] pyrene-7, 8-dihydrodiol-9, 10-epoxide (BPDE) and cross-linking agent mitomycin C (MMC) were selected. SDS-PAGE and immunoblotting were used to examine the protein levels of GRP78/BiP, GDADD153/CHOP and activation state of endoplasmic reticulum located caspase-12 in FL cells before and after MNNG, BPDE or MMC exposure. RESULTS: Immunoblotting showed that the protein level of endoplasmic reticulum specific proteins GRP78/BiP and GADD153/CHOP were significantly increased and endoplasmic reticulum located caspase-12 was activated in low concentration of MNNG (0.25 and 1 ?mol/L) and BPDE (5 and 50 nmol/L)-treated cells. MMC at all of the three concentration used (5, 50 and 500 ?mol/L) decreased the expression of GRP78/BiP, while it has no effects on CHOP and caspase-12. CONCLUSIONS: Both low concentration MNNG and BPDE could trigger the ER-stress in the exposed cells, while MMC could induce the down-regulation of the GRP78/BiP protein, which plays an important mediating role in the induction of ER-stress and may thus change the responsiveness against ER-stress inducers. It is suggested that ER-stress might partially mediate the cellular responses excited by exposure to some DNA-damaging agents/carcinogens.

The major role of DNA polymerase ? was thought to be limited in its involvement in short patch base excision repair by removing 5'-deoxyribose phosphate and base insertion. However, the recent researches indicate that polymerase ? might take part in a wide spectrum of DNA metabolism reactions, including long patch base excision repair, DNA replication, recombination, meiosis and transleisional DNA synthesis. Because of its wide and important cellular function, an inappropriate intracellular polymerase ? level might be associated with genomic instability. Down-regulation or mutation of polymerase ? is mutagenic due to deficient in DNA repair, while overexpression of this error-prone ? polymerase might perturb the normal function of other accurate polymerases and cause genomic instability as well.

AIM: To establish cell line FL-POL? - and to study the role of POL?(polymerase kappa) on genetic stability. METHODS: A mammalian expression vector expressing antisense POL? gene fragment pMAMneo -amp -- POL? was constructed by cloning the 1 690-1 918 fragment of POL? gene into the mammalian expression vector pMAMneo-amp - in antisense orientation. FL cells were fransfected with this antisense RNA expressing vector and selected by G418. Based on the shuttle-plasmid pZ189, the mutation assay was made. RESULTS: The spontaneous mutation frequency of supF tRNA gene in the plasmid replicated in the FL-POL? - was 11.2?10 -4 , while it was 4.9?10 -4 and 3.7?10 -4 in the control cells FL and FL-M , respectively. CONCLUSION: POL? playes an important role in maintenance of genetic stability.

Gene transcriptional regulation research is one of the major challenges in the post-genome era. Bioinformatics has become more important with the rapid accumulation of complete genome sequences and the advances of computational methods and related databases. The current computational approaches in promoter prediction, transcription factor binding site identification, composite elements prediction, co-regulation of gene expression analysis and phylogenetic footprinting in the regulatory region analysis are discussed in this review.

The 5-methylcytosine (~mC) in DNAs from 5-azacytidine and MNNG treated FL, Wish and Veto-E6 ceUs were analysed by HPLC. In 2?10~(-6)mol/L 5-azaCR treated cells, the percentages of ~mC in total cytosine were all lowered significantly (P 0.05). These results were in good agreement with those obtained by radioactivity analysis of newly replicated DNA fragments from Hpa Ⅱ digest. These results further validate the idea that DNA hypomethylation as a general pathway in the initiation process of chemical carcinogenesis is based on the results obtained by a defectively designed experiment.