Initial Dipeptide Formation in Hemoglobin Biosynthesis
Abstract
Initiation factors M1 + M2 from reticulocyte ribosomes bind Met-tRNAF to rabbit reticulocyte ribosomes containing endogenous hemoglobin mRNA. The initial binding of Met-tRNAF appears to be to the small ribosomal subunit. The Met-tRNAF is able to participate in what is presumed to be the first peptide bond in the formation of hemoglobin, namely the synthesis of a methionyl-valine dipeptide. The formation of this methionyl-valine dipeptide requires Met-tRNAF, initiation factors M1, M2, and M3, as well as Val-tRNA and T1. No synthesis of methionyl-valine dipeptide takes place if Met-tRNAF is replaced by Met-tRNAM, or if initiation factor M3 is omitted. Thus, Met-tRNAF appears to be the initiator tRNA for hemoglobin biosynthesis and M3, although required for the synthesis of the first peptide bond of hemoglobin, does not appear to be necessary, under the experimental conditions studied, for Met-tRNAF binding.
