AN INFB-HOMOLOG IN SULFOLOBUS-ACIDOCALDARIUS

We have identified an archaeal homologue of the bacterial translation initiation factor 2(IF-2 or infB) in a partial open reading frame situ ated upstream of the gene cluster coding for the large subunits of the DNA-dependent RNA polymerase (RNAP) in Sulfolobus acidocaldarius. Bas ed on this similrity, a larger genomic clone of this region was isolat ed and sequenced. Although the putative Sulfolobus translation factor gene is highly similar to infB, it shares an even higher degree of sim ilarity with the recently described FUN12 gene from Saccharomyces cere visiae. Phylogenetic trees inferred from sequences of homologous trans lation initiation, elongation and termination factors confirm that bot h the new Sulfolobus gene and yeast FUN12 are members of the IF-2 fami ly and that the root of the IF-2 subtree determined within a 3-fold ro oted universal treee of IF-2, EF-1 alpha/Tu and EF-2/G strongly suppor ts a close phylogenetic relationship between the archaea and the eukar yotes. The genomic context of the Sulfolobus infB also reveals links b etween two highly conserved bacterial gene clusters, the RNAP operon a nd the nusA-infB operon. In bacteria these operons are not linked, but the location of the Sulfolobus infB- and nusA-homologues immediately upstream and downstream of the RNAP gene cluster, respectively, links the two conserved bacterial operons and may indicate an ancient genome reorganization.