Protein initiation without folate in Streptococcus faecium

NH2-Terminal Amino Acid Distribution and Amino Acid Composition ofStreptococcus faecalisR Soluble and Ribosomal Proteins

“…Methionine and alanine account for 71 to 84% of the observed end groups depending upon the culture conditions of the cells from which the proteins were obtained, yet those two residues only comprise about 13% of the total amino acid residues in the protein mixtures analyzed. The amino acids found at the termini of S. faecalis proteins are in most cases qualitatively similar to those reported for several other organisms, however, quantitatively the frequency of particular end groups varies markedly between certain organisms (8,25,26,30,40,41).…”

“…With the exception of certain folate-requiring Lactobacteriacae, the initiation of protein synthesis in bacterial systems involves in most, if not all, cases formylated methionyl-tRNA,Met (11,17). The presence of the formyl group is thought to contribute to the increased levels of NH2-terminal methionine observed in prokaryotes (8,25,30,40,41) as compared to the low levels of end group methionine detected in eukaryotes (26,30). In bacteria utilizing formylmethionine, deformylation must occur prior to cleavage of terminal residues by aminopeptidases (1,13,38).…”

“…Proteins, in spite of their complexity and heterogeneity with respect to primary structure, possess a relatively simple NH2-terminal amino acid distribution (8,25,26,30,40,41). The absence of a random distribution of amino acid residues occupying the NH2-terminal position of both soluble and ribosomal proteins, first discovered by Waller and Harris in studies with Escherichia coli (40,41), appears to be a manifestation of the mechanism by which polypeptide chains are synthesized in vivo: from the amino-terminal end to the carboxyl-terminal end of the molecule.…”

“…Most cellular proteins undergo proteolytic processing sometime after the initiation phase of polypeptide chain biosynthesis so that amino acid residues other than methionine or formylmethionine commonly occur in the NH,-terminal position of mature cellular proteins. Methionine, alanine, serine, threonine, and aspartic and glutamic acids are observed most frequently as the major NH2-termini in prokaryotic organisms (8,25,30,40,41), and alanine, glycine, serine, threonine, and aspartic and glutamic acids most often in eukaryotic organisms (26,30).…”

One‐carbon metabolism, folate, zinc and translation

“…Their anabolic role was emphasized by the fact that the corresponding redox reactions depended on NADP, not NAD (Albrecht et al , 1968). Early experiments made also apparent that in organisms such as Streptococcus faecium , translation initiation in the absence of folate did not require this formylation step (Pine et al , 1969). Casting some doubt about the significance of the modification, this observation triggered a number of studies that explored the conditions under which formylation was apparently essential.…”