Gene regulation in N mutants of bacteriophage lambda

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacteriophage lambda's N gene product is essential for growth on wild-type Escherichia coli.
• N gene mutants (N(-)nin) do not plate on recA bacterial mutants.
• Secondary mutations conferring recA+ phenotype are located in the immunity region, resembling cro mutants.

Purpose of the Study:

• To investigate the genetic basis of bacteriophage lambda's growth on recA mutants.
• To characterize the function of the cro gene in relation to N gene function and recA interactions.
• To understand the regulation of gene expression and excision in bacteriophage lambda.

Main Methods:

• Isolation and characterization of secondary mutants of bacteriophage lambda.
• Phenotypic analysis of N(-)nin and N(-)cro mutants on recA and wild-type E. coli.
• Assessment of lambda exonuclease production.
• Evaluation of phage excision rates from lysogens.
• Testing for exclusion by P2 prophage.

Main Results:

• N(-)nin mutants do not plate on recA bacteria.
• Secondary mutants selected for recA+ growth map to the immunity region and are phenotypically similar to cro mutants.
• In N(+) phage, cro mutations enhance lambda exonuclease production.
• N(-)cro phages lack detectable exonuclease, exhibit increased specific excision, and are excluded by P2 prophage.
• N(-)cro phages express genes left of N at a low but increased rate compared to N(-)cro(+) phages.
• N(-)nin phages show immeasurably low specific excision rates.

Conclusions:

• The cro gene plays a significant role in regulating bacteriophage lambda growth, particularly in recA mutant backgrounds.
• N(-)cro mutants display altered gene expression and excision, suggesting cro's involvement in coordinating these processes.
• The ability to plate on recA is linked to specific regulatory mutations affecting gene expression and phage lifecycle.