The role of ribosomal proteins L7 and L-12 in polypeptide chain initiation in Escherichia coli.

Proteins L, and LIZ from the 50 S ribosomal subunit are required for polypeptide chain initiation in Escherchia 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 L? or LlZ. N-Formyl methionyl transfer RNA binding to ribosomes is also impaired in the absence of L7 and LIZ. The results indicate that L7 or LIZ is required for the catalytic function of IF-Z in binding N-formyl methionyl transfer RNA to ribosomes. In each reaction tested, L7 and LIZ are about equal in efficiency in restoring activity to depleted 50 S subunits. These results are discussed in light of the current information on the role of these ribosomal proteins in other partial reactions or protein synthesis.