| Research Abstract |
It has been known that mutations are induced upon DNA damage. Recently, a new type of DNA polymerases (Pols) that are capable of bypassing DNA damaged sites has been identified. These enzymes do not have a proofreading 3'-5' exonuclease activity, and as the result, they are error-prone. For preventing mutations, they should be tightly regulated, so as to exhibit their activities only when needed. We have identified one of such enzymes in mice, Polκ. The Polk gene encoding Polκ is expressed ubiquitously in many tissues, and most strongly in testis. We found that Polk-mRNA transcription is initiated at two different sites. The upstream one is utilized in most tissues, and the downstream one is utilized specifically in testis. Transcription of polk-mRNA in testis seemed to occur at almost equal frequencies from both sites. In testis, two species of Polk-mRNAs are found; testis-specific 3-kb mRNAs are predominant while 5-kb mRNAs commonly found in other tissues are also present, The difference between the two species is not due to the difference in the start site, rather due to the polyadenylation at different sites in the 3'-end. ARE sequence, which is known to render mRNA unstable when present in 3'-untranslated region, is present in the 5-kb mRNA at ten times, but it is absent in the 3-kb mRNAs. Therefore, it seems very likely that 3-kb mRNAs are more stable than the 5-kb mRNA, accumulating in testis.
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