Involvement of the host initiator function dnaA in the replication of coliphage lambda

Area of Science:

• Molecular Biology
• Virology
• Bacteriology

Background:

• Coliphage lambda DNA replication is a complex process involving host and phage factors.
• The host initiator protein DnaA is crucial for initiating DNA replication in E. coli.
• Lambdoid prophages, like Rac, can influence phage replication strategies.

Purpose of the Study:

• To investigate the role of the host dnaA function in coliphage lambda DNA replication initiation.
• To determine the influence of the Rac prophage on lambda DNA replication in the absence of functional dnaA.
• To elucidate the mechanism of replication mode switching from theta to sigma in lambda phage.

Main Methods:

• Utilizing dnaAts mutants and Rac+ strains of E. coli.
• Analyzing phage DNA replication patterns under different genetic conditions and temperatures.
• Observing replication initiation, theta replication, and sigma mode replication of lambda phage DNA.

Main Results:

• Lambda DNA replication initiation depends on host dnaA function when Rac is absent.
• The presence of Rac compensates for the absence of dnaA, initiating replication.
• In dnaAts rac+ cells, lambda DNA switches from theta to sigma replication, yielding high progeny.
• DnaA function blocks lambda Pts1 mutant replication, but Rac presence facilitates the theta to sigma switch.

Conclusions:

• Host dnaA function is essential for lambda DNA replication initiation, with Rac acting as a suppressor of dnaA dependence.
• The Rac prophage plays a significant role in modulating lambda DNA replication, promoting a switch to sigma mode.
• Incompatibility between DnaA and lambda Pts1 may occur during preprimosome insertion at the ori lambda site.