Mechanism of translational initiation in prokaryotes

Abstract
Initiation factor IF2 from either Escherichia coli or Bacillus stearothermophilus was found to possess the previously undetected property of stimulating the template‐dependent ribosomal binding of aminoacyl‐tRNAs with free α‐NH2 groups. IF1, which had no detectable activity alone, was found to stimulate the activity of E. coli IF2 and, to a lesser extent, that of B. stearothermophilus IF2. Since in the absence of ribosomes not even a weak interaction between the two IF2 molecules and the aminoacyl‐tRNAs was detected, the present findings indicate that IF2 can act at the ribosomal level stimulating aminoacyl‐tRNA binding without prior formation of a binary complex with the aminoacyl‐tRNA. IF2 does not appear to open or strengthen a weak A‐site binding, but rather to enhance aminoacyl‐tRNA binding to a 30 S site equivalent to the P‐site by slowing down the rate of aminoacyl‐tRNA dissociation from ribosomes.

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