Structural features that underlie the use of bacterial Met-tRNAfMet primarily as an elongator in eukaryotic protein synthesis.
Met-tRNAfMet from Escherichia coli is utilized efficiently as an elongator tRNA during protein synthesis in the rabbit reticulocyte lysate since it rapidly incorporates its methionyl residue into the same tryptic peptides of rabbit globin as the endogenous Met-tRNAmMet. Therefore, it must lack the structural characteristics that prevent the eukaryotic initiator tRNA from entering elongation. In contrast, E. coli Met-tRNAfMet appears to initiate very poorly since, unlike reticulocyte Met-tRNAiMet, it forms no detectable 43 S preinitiation complexes, and only a very small fraction of the methionine it contributes to polyribosomal peptidyl-tRNA is found at the N terminus. The bacterial fMet-tRNAfMet, which cannot elongate, is utilized for polypeptide chain initiation at a much lower level than the formylated Met-tRNAiMet from eukaryotes. The ability of E. coli Met-tRNAfMet to be used as an elongator and fMet-tRNAfMet as an initiator in the reticulocyte lysate may be considerably underestimated because of the rapid enzymatic hydrolysis of these initiator tRNAs in the lysate. The enzyme hydrolyzes fMet-tRNAfMet and Met-tRNAfMet from E. coli in a strictly Mg2+-dependent manner but not the corresponding species from yeast or rabbit reticulocytes. It also hydrolyzes yeast N-acetyl-Phe-tRNAPhe and reticulocyte peptidyl-tRNA, showing that this enzyme--like the eukaryotic protein synthetic machinery--does not readily distinguish the bacterial tRNAfMet from eukaryotic elongator tRNA.
Wagner
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T
Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
Rundquist
C
C
Gross
M
M
Sigler
P B
PB
D000818:Animals; D004926:Escherichia coli / Q000235:genetics*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D005914:Globins / Q000096:biosynthesis; D006160:Guanosine Triphosphate / Q000378:metabolism; D006867:Hydrolases / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010441:Peptide Chain Elongation, Translational / Q000502:physiology*; D010446:Peptide Fragments / Q000378:metabolism; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000378:metabolism*; D012331:RNA, Fungal / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D012358:RNA, Transfer, Met; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014357:Trypsin
D015852:Eukaryotic Initiation Factor-2; D010446:Peptide Fragments; D012329:RNA, Bacterial; D012331:RNA, Fungal; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; C026464:tRNA(m)(Met), methionine-; C024988:tRNA, formylmethionine-; D006160:Guanosine Triphosphate; D005914:Globins; D008715:Methionine; D006867:Hydrolases; D014357:Trypsin