GATC Methylation by Dam methylase in archaea: its roles and possible transcription regulation by an FFRP

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Methylation of pairs of adenines at their N6 positions in GATC sites (GATC methylation) in archaeal genomic DNAs has been studied. Genomic DNAs in cells of three archaeal species were found as fully methylated, while those of four other archaeal species were free of such methylation. Consistently with this pattern of the presence or absence of GATC methylation, homologues of E. coli Dam methylase was found present or absent, but various other types of DNA methylases were not. A Dam homologue from Pyrococcus sp. OT3 was expressed and its expected function of methylating GATC was confirmed. By methylation of each adenine the DNA duplex was destabilized by 0.56 ± 0.10 Kcal/mol, and this effect was additive. For some archaea, transcription regulation of Dam methylase gene appears to be needed upon cell replication, and in regions upstream of three Dam methylase genes, nucleotide sequences close to TTTTCTTTGAAAA were present. This arrangement, five bases each at the ends, which are complementary to each other, sandwiching three T bases at the center, fits into a pattern the same as those recognized by dimers of transcription factors, feast/famine regulatory proteins (FFRPs). (Communicated by Masanori OTSUKA, M.J.A.)
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