Functional analysis of an alkyltransferase-like protein by DNA microarray

O6-methylguanine (O6-meG) is a potentially mutagenic and toxic lesion in DNA. O6-meG is caused by certain classes of carcinogenic and chemotherapeutic alkylating agents. Repair process of this lesion is thus notable in both the etiology and treatment of cancer. It is well known that the biological effects of such alkylating agents can be extensively prevented by the highly conserved DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT). AGT repairs O6-meG damage in DNA by the stoichiometric and auto-inactivating transfer of the methyl group to a cysteine residue in its active site (PCHRV). Sequence alignment analysis shows the existence of a group of alkyltransferase homologues in which the cysteine residue in the putative active site has been replaced with other residues. These proteins are defined as alkyltransferase-like (ATL) proteins. Thermus thermophilus HB8 has only ATL protein (TTHA1564) and lacks AGT. In organisms that have only ATL protein and lacks AGT, the repair pathway of alkylated lesion is unknown because ATL protein has no cysteine residue needed to transfer the methyl group of O6-meG. Therefore, we expect that a novel pathway exists for repair of alkylated lesion. It is suggested that TTHA1564 recognizes O6-meG in DNA and interacts with some proteins (Table 1). Based on these results, we made a hypothesis that ATL protein initially recognizes O6-meG in DNA as a damage sensor, and then recruits other proteins involved in repair of alkylated lesion. In order to verify this hypothesis, we performed DNA microarray to investigate gene expression pattern of wild-type and TTHA1564 disruptant in the presence of an alkylating agent, N-methyl-N'-nitro-N-nitrosoguanidine. In this poster, we discuss the result of DNA microarray analysis.