R-factor-mediated nuclease activity involved in thymineless elimination

Area of Science:

• Molecular Biology
• Bacteriology
• Virology

Background:

• Bacterial ligase plays a role in DNA replication and repair.
• R-factors are plasmids that can confer antibiotic resistance and affect host cell functions.
• Phage-T4 mutants deficient in ligase provide a tool to study host-plasmid interactions.

Purpose of the Study:

• To investigate the effect of R-factor 1818 (R-1818) on the propagation of ligase-deficient phage T4 mutants in Escherichia coli.
• To determine the influence of bacterial ligase levels and host cell conditions (thymine starvation, UV irradiation) on R-factor stability and phage propagation.

Main Methods:

• Assessing the efficiency of plating and burst size of ligase-deficient phage T4 mutants on various E. coli strains with different ligase levels.
• Manipulating host cell conditions through thymine starvation and ultraviolet irradiation.
• Monitoring R-factor elimination under different experimental conditions.

Main Results:

• R-1818 did not affect phage plating efficiency in E. coli with normal, excess, or defective ligase.
• Thymine starvation of ligase-overproducing E. coli significantly reduced phage propagation compared to ligase-deficient strains.
• UV irradiation increased phage burst size on ligase-overproducing strains versus ligase-deficient ones.
• R-factor elimination by thymine starvation was inversely correlated with host ligase levels.
• UV irradiation caused R-factor elimination in strains with excess or defective ligase, but not wild-type ligase levels.

Conclusions:

• R-1818 likely encodes a nuclease induced by thymine starvation.
• This nuclease, potentially working with host nucleases, mediates R-factor elimination under thymine starvation.
• Host ligase levels modulate R-factor stability and response to environmental stresses like UV irradiation.