A SURVEY OF POLYPEPTIDE DEFORMYLASE FUNCTION THROUGHOUT THE EUBACTERIAL LINEAGE

N-terminal formylation of ribosome-synthesized polypeptides is assumed to be among the most conserved features that distinguish the eubacter ial line of descent from other living phyla. In order to assess the an cientness of this trait, def genes encoding polypeptide deformylase we re characterized from four eubacterial species, Lactococcus lactis, Ba cillus subtilis, Calothrix PCC7601 and Thermotoga maritima, taking adv antage of the conditional viability of the def mutants of Escherichia coli. Altogether, eight sequences of polypeptide deformylase have been obtained from all the eubacterial sources which were investigated, ei ther through systematic genome sequence analysis or through genetic sc reening, yielding a highly homologous family. A gene putatively encodi ng Met-tRNAi formyltransferase, fmt, was found downstream of the defor mylase gene except in L. lactis, Mycoplasma genitalium, Calothrix PCC7 601 and T. maritima. These results argue strongly for the ancestral ch aracter of N-terminal formylation in eubacteria. Most of the wide devi ations of amino acid usage observed in def- and fmt-encoded proteins a mong species is best accounted for by the nucleotide composition of ge nomes. Furthermore, the species of origin of each protein appears to b e more recognizable than its function, considering only its amino acid composition. (C) 1997 Academic Press Limited.