Insertion sequence IS2 associated with int-constitutive mutants of bacteriophage lambda

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Bacteriophage lambda integrates into the host genome via a site-specific recombination mechanism.',
• The int gene encodes the integrase protein, essential for lambda integration.',
• Regulation of int gene expression is crucial for controlling lysogeny and lytic cycles.

Purpose of the Study:

• To investigate bacteriophage lambda mutations conferring elevated constitutive expression of the int gene (int-c mutations).
• To elucidate the molecular mechanisms underlying constitutive int gene expression in these mutants.

Main Methods:

• Genetic mapping of int-c mutations.
• Analysis of IS2 insertion sequences in specific mutant classes.
• Inference of transcriptional regulation mechanisms based on mutation location and known regulatory elements (pI-tI leader, cII, cIII products).

Main Results:

• Two classes of int-c mutations were identified.
• Class one mutations, mapping between b538 and bio386, appear to be point mutations inactivating the tI terminator signal.
• Class two mutations involve IS2 insertion in orientation II between the int gene and the b538 endpoint, suggesting a novel promoter.
• Most int-c mutations are located within the xis gene, with one exception (int-c548) possibly between int and xis.

Conclusions:

• Point mutations in class one directly affect the pI-tI leader RNA, leading to constitutive int expression independent of cII and cIII.
• IS2 insertion in class two mutants creates a new constitutive promoter, driving int transcription.
• These findings provide insights into the complex transcriptional regulation of the bacteriophage lambda int gene.