Posttranscriptional control of bacteriophage lambda gene expression from a site distal to the gene.

Abstract

The bacteriophage A int gene product, integrase, recombines the phage DNA with the host DNA at specific sites on each to accomplish lysogeny. The int gene is transcribed from two promoters, PL and PI, each regulated positively by A proteins. The expression of integrase is also controlled from a site, sib, in the b region of the phage genome. This is a unique regulatory site because it is located distal to the structural gene in relation to the promoters. The expression ofint from the PL promoter is inhibited when sib is present. This effect appears to be specific for PL because sib does not cause inhibition of PI-dependent int synthesis.A mutants that contain alterations in the site have been isolated. Sequence analyses of the mutations reveal single base changes, spanning 37 base pairs (bp) in the b region, some 240-bp beyond the int gene. Another mutant, hef13, which has a phenotype similar to that of sib, introduces a nucleotide change within the same 37-bp region. The sib and hefmutatsons cluster within a region of dyad symmetry. Regulation of int synthesis by sib occurs after transcription.of the int gene. There is no difference in the rate of .PL'promoted int mRNA synthesis in either sib' or sib-phage infections, yet int mRNA is less stable in the sib' infection. Because RNase 111 host mutants are defective in sib regulation, processing of the PL mRNA at sib by this endoribonuclease may cause int mRNA decay and decrease int synthesis.Bacteriophage A inserts its DNA into the Escherichia coli chromosome as part of the process leading to lysogeny. This integration event uses A int protein and occurs by reciprocal recombination at specific locations, named "attachment sites," in the phage (attP) and in the bacterial (attB) DNAs. The reversal of the integrative reaction is excision; this process occurs after prophage induction and allows the integrated DNA to dissociate from the bacterial chromosome. The two phage proteins int and xis are required for excisive recombination. Host factors are also required for both integration and excision, but the direction of the reaction depends primarily upon the presence of int or int and xis in the cell (1-3).Two promoters, PI and PL, control transcription of the 1.5-kilobase int-xis region (4, 5) (Fig. 1). Both promoters are positively regulated by different effectors. Gene N product allows elongation of the PL transcript through several genes into the int-xis region (11,12). The cII product is required to initiate transcription from PI by facilitating initiation by RNA polymerase (7). The PI promoter overlaps with the xis gene, and its transcript does not include all of xis (8-10). Thus a differential expression of the integration and excision systems is assured by turning on and off PI or PL Infections with cII-phage result in decreased int protein levels and integration activity (13)(14)(15). This result is unexpected because transcription initiated by RNA polymerase at PL was thought to extend through thexis-int region (11, 16). However, infection with b2cII-...

Control and Regulation of KplE1 Prophage Site-specific Recombination

“…Control of the integrase gene expression is part of the genetic switch that leads to the completion of the lytic cycle. In the prophage, the int gene is under the control of two promoters P I and P L and is differentially regulated by a retroregulation process that involves mRNA processing (2,45,46). In prophage, the P L promoter is controlled by antitermination and allows the expression of xis and int genes in lytic conditions; in contrast the P I promoter is under positive regulation by CII protein and is located inside the xis gene.…”

Self-regulation of 70-kilodalton heat shock proteins in Saccharomyces cerevisiae.

“…This hybrid gene may not contain all of the signals that are required for SSAI selfregulation. Additional cis-acting regulatory elements might lie within the SSAI coding region, as found in the mammalian 1-tubulin gene (14), or downstream of its 3' terminus, as in the case of the lambda itlt gene (15).…”

Little Lambda, Who Made Thee?

“…2) (reviewed in references 49 and 83). The two key regulatory elements are sib, a site of endonucleolytic RNase cleavage that is located promoter distal to int (86), and N, a protein that suppresses termination of certain phage transcripts (see The Story of N, below). Transcripts that initiate at the P L promoter contain the sib sequence because termination is suppressed by N. These transcripts are therefore cleaved, and processive exonucleolytic degradation of the upstream RNA destabilizes the int message.…”