Specificity of protein synthesis by bacterial ribosomes and initiation factors: Absence of change after phage T4 infection

Using several natural messenger RNA's-f2 RNA, Qβ RNA, T7 RNA, T4 early mRNA, T4 late mRNA and Escherichia coli RNA-ribosomes isolated from cells either 5 or 12 minutes after T4 infection direct synthesis of only 35 to 70% as much protein as do ribosomes from uninfected cells. However, with poly(U) or formaldehyde-treated f2 RNA message, both types of ribosomes work equally well. Experiments mixing salt-washed ribosomes and initiation factors from these cells show, in agreement with work of others, that the reduction with natural messages is due only to changes in the initiation factors. As shown by peptide mapping of protein made in vitro and labeled with N-formyl [³⁵S]methionyl-transfer RNA, T4 and control ribosomes direct initiation, using f2 RNA, Qβ RNA, early and late T4 mRNA and T7 RNA, of the same polypeptides, in about the same relative proportions. We conclude that there is no change in the specificity of initiation factors after T4 infection; alterations in the amounts of factors are probably not essential either for shut-off of host protein synthesis or for the transition from early to late T4 protein synthesis.