Abstract
Many types of DNA damage block replication fork progression during DNA synthesis because replicative DNA polymerases are unable to bypass altered DNA bases. To overcome this block, cells employ specialized translesion synthesis (TLS) polymerases, which can insert nucleotides opposite damaged bases. The TLS polymerases are also characterized in terms of their low-fidelity synthesis on undamaged DNA, leading to the prediction that unregulated action of these polymerases give deleterious effects on cells. Thus, activity of these polymerases must be regulated strictly. In fact the amount of TLS polymerase is kept constant at protein level even if the level of RNA increased more than 30 times by ectopic expression in fly. By deletion analysis of dRAD30B we have identified a region responsible for degradation of this protein. When the region was deleted, stability of he truncated protein increased drastically. The degradation is inhibited by treatment with MG132 and Epoxomicin, suggesting an involvement of ubiquitin-proteasome pathway on the regulation of dRAD30B stability. Another new finding is the lethal phenotype of RNAi over-expression transgenic fly. We have established transgenic fly lines, in which expression of Rad30A, B and Rev1 RNAi construct is regulated under control of GAL4-inducible UAS promoter. Although induction of the RNAi construct only in eye by tissue-specific driver show no phenotype, induction in whole body by Actin-driver show pupal lethality. This phenotype was relieved by crossing the RNAi fly with cDNA over-expressing fly.
