Selection for mutations in the PR promoter of bacteriophage lambda

Area of Science:

• Molecular Biology
• Bacteriophage Genetics
• Promoter Function

Background:

• The early rightward promoter (PR) of bacteriophage lambda is crucial for viral gene expression.
• PR's insertion into M13-derived vectors can cause lethality if transcription is directed towards the M13 origin of replication (ori).
• Lethality is associated with transcriptional interference or other mechanisms impacting vector replication.

Purpose of the Study:

• To investigate the lethality associated with PR insertion in M13 vectors.
• To develop and apply a method for isolating mutations within the PR sequence.
• To demonstrate the general applicability of in vivo promoter mutant isolation.

Main Methods:

• Utilized M13-derived vectors containing the bacteriophage lambda PR.
• Introduced mutations into the PR sequence.
• Employed a selection strategy based on plaque formation in the absence of lambda cl repressor.
• Isolated and characterized 14 distinct mutations at 8 different sites within PR.

Main Results:

• Confirmed that PR insertion is lethal to M13 vectors when transcription is oriented towards the origin of replication.
• Successfully isolated 14 mutations in PR that alleviate this lethality.
• Demonstrated that mutations, promoter repression (by lambda cl repressor), or transcription termination can relieve the lethal phenotype.
• Validated a novel in vivo method for isolating promoter mutants.

Conclusions:

• The orientation of transcription from strong promoters like lambda's PR relative to replication origins is critical for vector stability.
• In vivo selection provides an effective strategy for generating and isolating promoter mutants.
• This methodology is broadly applicable to studying other regulated promoters.