Multiple regulatory mechanisms controlling phage-plasmid P4 propagation

Abstract

Bacteriophage 1'4 autonomous replication may result in the lyric cycle or in plasmid maintenance, depending, respectively, on the presence or absence of the helper phage P2 genome in the Escherichia coil host cell. Alternatively, P4 may lysogenize the bacterial host and be mainta/ned in an immune-integrated condition. A key step in the choice between the lytic/plasmid vs. the lysogenic condition is the regulation of 1'4 t~ eperon. This operon may be transcribed from two promoters, PL~ and PLL, and encodes both immunity (promoter proximal)and replication (promoter distal) functions. PLE is a constitutive promoter and transcription of the downstream replication genes is regulated by transcription termination. The trans-acting immunity factor that controls premature transcription termination is a short RNA encoded in the PtE proximal part of the operon. Expression of the replication functions in the lytic/plasmid condition is achieved by activation of the PLL promoter. Transcription from PLt is insensitive to the termination mechanism that acts on transcription starting from PLE" PLL is also negatively regulated by 1'4 off88, the first gene downstream of l%L. An additional control on P4 DNA replication is exerted by the P4 car gene product.

Derepression of prophage P2 by satellite phage P4: cloning of the P4 epsilon gene and identification of its product

“…However, 20 min after P4 ash9 infection, as opposed to P4 ash9 εam104 infection, a 10-kDa protein has been detected, which implies that the ash9 mutation affects the expression of ε (22). During P4 lytic growth, transcription from the constitutive promoter Ple occurs only for a short time, since this transcript contains the trans-acting immunity factor that controls premature transcriptional termination of the Ple transcript (18). The upstream Pll promoter is activated instead, and as the Pll transcript is insensitive to the termination mechanisms, it proceeds through the whole ␣ operon, allowing P4 replication (13,14).…”

“…The upstream Pll promoter is activated instead, and as the Pll transcript is insensitive to the termination mechanisms, it proceeds through the whole ␣ operon, allowing P4 replication (13,14). The Pll transcript, as opposed to the Ple transcript, does not have an untranslated leader region, which may account for its insensitivity to the immunity factor (18). The P4 fragment cloned into plasmid pEE804 mimics the transcript from Pll, since the ε leader sequence is translated.…”

The Floating (Pathogenicity) Island: A Genomic Dessert

“…All known SaPI ori s consist of two sets of short iterons flanking an ~80 bp AT-rich region [18]. The Rep protein, like typical phage initiators [19], has helicase activity, which is required for initiation [18]. The Rep-ori interaction is SaPI-specific and is determined by a matching interaction between the iterons and a specificity determinant in the Rep C-terminus [18].…”

Multiple initiation mechanisms adapt phage T4 DNA replication to physiological changes during T4's development

“…More recently, a role of uncharged tRNA was described in .qtabilig~ng ~pecific RNA anti-termination structures in B. subtili~ [55]. The RNA-mediated transcriptional regulation of phages P1 and P4, discussed in this issue [56,57,63,64], are particularly striking examl~les of structural roles of complementary RNA segments interacting in alternative pairings to regulate l~hysiological processes. The function of wedge RIqA in initiation of phage T4 DNA replication is a novel variation on this theme.…”