Polarity within pM and pE promoted phage lambda cI-rexA-rexB transcription and its suppression

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• The bacteriophage lambda cI-rexA-rexB operon controls immunity and Rex exclusion phenotypes in lysogenic cells.
• Immunity relies on the CI repressor, while Rex exclusion of T4rII mutants requires RexA and RexB proteins.
• Temperature-sensitive mutations in cI result in conditional Imm and Rex phenotypes.

Purpose of the Study:

• To investigate the transcriptional polarity within the cI-rexA-rexB operon.
• To understand the regulation of RexA and RexB protein expression.
• To identify host factors involved in Rex phenotype regulation.

Main Methods:

• Construction of plasmids expressing cI-rexA-rexB from non-lambda promoters.
• Analysis of transcriptional polarity using temperature-sensitive and wild-type cI alleles.
• Introduction of host rho and other mutations to assess their effect on polarity and Rex phenotype.
• Investigating the role of 10Sa RNA and ClpXP in protein degradation.

Main Results:

• Transcriptional polarity was observed within the cI-rexA-rexB operon, particularly when the CI repressor was nonfunctional.
• Host rho factor and specific host mutations (ssrA, clpP) suppressed polar effects.
• Suppression by ssrA and clpP mutations suggests RexA/RexB are targeted for degradation by the 10Sa RNA-ClpXP system under polar conditions.

Conclusions:

• Transcriptional polarity significantly impacts Rex protein expression in bacteriophage lambda.
• Host factors, including rho and the 10Sa RNA-ClpXP degradation pathway, play crucial roles in regulating Rex phenotype.
• Understanding these regulatory mechanisms is vital for comprehending phage-host interactions.