Mutants of T7 bacteriophage inhibited by lambda prophage.

Area of Science:

• Bacteriophage genetics
• Molecular biology
• Virology

Background:

• T7 phage is a model organism for studying viral replication.
• Lambda lysogens are bacterial cells infected with lambda phage, providing a specific host environment.
• Gene 20 of T7 phage has been identified as crucial for phage development.

Purpose of the Study:

• To characterize the function of the T7 phage gene 20.
• To investigate the interaction between T7 gene 20 and lambda lysogens.
• To understand the role of gene 20 in T7 DNA packaging.

Main Methods:

• Isolation and characterization of T7 gene 20 mutants (including amber mutants).
• Complementation studies with T7 ligase mutants.
• Analysis of T7 DNA synthesis and packaging in infected lambda lysogens.
• Identification of host mutations affecting T7 growth.

Main Results:

• T7 gene 20 mutants exhibit a conditional lethal phenotype, unable to propagate on rex+ lambda lysogens.
• Gene 20 mutants suppress T7 ligase mutations, but not vice versa, suggesting a sequential role in infection.
• Host mutations can restore the growth of T7 gene 20 mutants on lambda lysogens.
• T7 DNA synthesis is normal in mutants, but DNA packaging into phage heads is blocked.
• The gene 20 protein is active in in vitro complementation and functions late in infection for DNA packaging.

Conclusions:

• T7 gene 20 encodes a protein essential for the late stage of phage assembly, specifically DNA packaging.
• The interaction with lambda lysogens highlights specific host-phage dependencies.
• Gene 20 function is distinct from T7 ligase, with gene 20 acting downstream.
• Further research into host-bacteriophage interactions can reveal new genetic pathways.