The role of ribosomal proteins L₇ and L₁₂ in polypeptide chain initiation in Escherichia coli

Proteins L₇ and L₁₂ from the 50 S ribosomal subunit are required for polypeptide chain initiation in Escherichia coli. Ribosomes deficient in these proteins cannot participate in initiation factor IF 2 dependent hydrolysis of guanosine triphosphate (either 'coupled' or 'uncoupled' from initiation); activity can be restored by the addition of either L₇ or L₁₂. N Formyl methionyl transfer RNA binding to ribosomes is also impaired in the absence of L₇ and L₁₂. The results indicate that L₇ or L₁₂ is required for the catalytic function of IF 2 in binding N formyl methionyl transfer RNA to ribosomes. In each reaction tested, L₇ and L₁₂ are about equal in efficiency in restoring activity to depleted 50 S subunits. These results are discussed in the light of the current information on the role of these ribosomal proteins in other partial reactions or protein synthesis.