JBC, Vol. 250, Issue 8, 3074-3079, Apr, 1975
Comparison of fMet-tRNAf and Met-tRNAf from Escherichia coli and rabbit liver in initiation of hemoglobin synthesis
N. A. Elson, S. L. Adams, W. C. Merrick, B. Safer and W. F. Anderson
A comparison has been made of the ability of the formylated and
unformylated initiator tRNAs of Escherichia coli and rabbit liver to
participate in a number of model reactions of protein synthesis. These
reactions include: (a) formation of a ternary complex composed of the
initiator tRNA, GTP, and initiation factor MP; (b) ApUpG-directed binding
of the initiator tRNA to 40 S subunits with initiation factor Ml; (c)
formation of the artificial dipeptide, methionylpuromycin; (d) formation of
the natural initial globin dipeptide, methionylvaline; and (e) synthesis of
sheep alpha and betaB-globin chains on reticulocyte polysomes from a type
BB sheep. The results of these studies indicate that although the
prokaryotic initiator tRNA species function efficiently in the partial
reactions which involve only binding, the methionine donated by the
prokaryotic tRNA is not incorporated efficiently into peptide linkage. This
suggests that the initial high level of binding of the E. coli initiator
tRNAs may be nonspecific, and that the structure of the tRNA itself is
important for specific recognition by eukaryotic initiation factors. The
effect of formylation on the effectiveness of the initiator tRNA is not
clear; it reduces activity in ternary complex formation, does not affect
ApUpG-directed binding to 40 S subunits, and increases the rate or extent
of incorporation of methionine, or both, into methionylpuromycin and globin
chains.
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