Abstract
The S gene of bacteriophage lambda (λ) has two AUG codons in the first three codons of the 107-codon reading frame. In this work, it is shown that both codons are used for translational initiation events in vitro and in vivo. These initiations result in the protein products designated S[107] (initiated at codon 1) and S[105] (initiated at codon 3), differing only in the amino-terminal sequence. Moreover, the timing of lysis in vivo is strictly correlated with the partition of initiation events assayed in vitro with 30S ribosomes and purified mRNA from wild type and modified S alleles. When the RNA supports more initiations at Met[1], lysis is abolished or delayed; when Met[3] is favored, lysis onset occurs more rapidly. These data support the notion that S[105] and S[107] have opposing roles in lysis, the former acting as a lysis effector and the latter as a lysis inhibitor. An analogous system has been identified in the lysis gene 13 of the Salmonella phage P22. This gene begins with the sequence Met[1]-Lys[2]-Lys[3]-Met[4]- ..., similar to the Met[1]-Lys[2]-Met[3]- ... motif of S. Here, it is shown that the two Met codons of P22 serve the same roles as Met[2] and Met[3] of S. In vitro analysis of the relative ribosome binding affinity for these two initiation sites indicates that the 13[108] product (Met[1] initiation) is produced at a lower stoichiometry relative to 13[105] (Met[4] initiation) than in the case of the two λ S proteins, suggesting that the 13 inhibitor product is more potent. The existence of a host RNA-binding activity is demonstrated by RNA gel mobility-shift assays and shown to have binding-specificity for the S mRNA. The protein is partially purified by gel filtration chromatography and shown to have a monomeric mass of approximately 60-65 kd. The binding site has been localized to the 200 nt region upstream of the sdi (structure directed initiation) structure which abuts the 5' region of the S reading frame. Preliminary experiments indicate the binding event may protect the RNA immediately adjacent to the sdi locus.
Nam, Kiebang (1991). Translational regulation of the S gene of bacteriophage lambda. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1284285.