A −1 Ribosomal Frameshift in the Transcript That Encodes the Major Head Protein of Bacteriophage A2 Mediates Biosynthesis of a Second Essential Component of the Capsid

摘要: A2 is a temperate bacteriophage that infects strains of several Lactobacillus casei-related species, including some used as probiotic components in fermented milks. It belongs to the family Siphoviridae, and its genome lies double-stranded DNA molecule 43,411 bp long which encodes 61 open reading frames (ORFs) presents 3′-protruding cohesive ends (15). These may be grouped into functional modules. Towards center region regulates switch between lytic lysogenic cycles. Here, two adjacent, divergently oriented repressor genes, cI cro, encode proteins play roles superficially similar those analogous lambda (14, 18-20). Downstream located cassette mediates integration phage chromosome hosts (2), while cro followed by replication module (27). this there stretch series small polypeptides, most are unessential for development or lysogenization phage, at least under laboratory conditions (15, 20). This end occupied terminase subunit determinant, marks beginning morphogenetic followed, towards other side ends, large (13) genes structural virion following order: capsid, head-tail connector, tail, host recognition, all form late-expressed, single operon Finally, lysis modules. Analysis revealed polypeptides 35 42 kDa (as judged from sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]) were major head ratio 4:1. Surprisingly, both shared their amino termini, matched an internal sequence orf5 genome. In line with finding, would originate different sizes, suffer same proteolytic processing upon incorporation capsid. render hypothetical 123-amino-acid polypeptide postulated scaffolding protein sizes found virions (15). In report, we confirm hypothesis through presentation data indicating protein, gp5A, corresponds translation product after processing, counterpart, gp5B, results change frame 85 acids longer than gp5A. Additionally, requirements frameshift occur revealed. it demonstrated essential generation viable phages. To our knowledge, first report −1 translational occurring gram-positive-specific bacteriophage, although analysis Listeria PSA suggests situation might more general (36). recent study, +1 frameshifts capsid tail reported.