We have identified an archaeal homologue of the bacterial translation initiation factor 2 (IF-2 or infB) in a partial open reading frame situated upstream of the gene cluster coding for the large subunits of the DNA-dependent RNA polymerase (RNAP) in Sulfolobus acidocaldarius. Based on this similarity, a larger genomic clone of this region was isolated and sequenced. Although the putative Sulfolobus translation factor gene is highly similar to infB, it shares an even higher degree of similarity with the recently described FUN12 gene from Saccbaromyces cerevisiae. Phylogenetic trees inferred from sequences of homologous translation initiation, elongation and termination factors confirm that both the new Sulfolobus gene and yeast FUN12 are members of the IF-2 family and that the root of the IF-2 subtree determined within a 3-fold rooted universal treee of IF-2, EF-1α/Tu and EF-2/G strongly supports a close phylogenetic relationship between the archaea and the eukaryotes. The genomic context of the Sulfolobus infB also reveals links between two highly conserved bacterial gene clusters, the RNAP operon and 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.