Genetic dissection of T4 lysis

Area of Science:

• Bacteriophage biology
• Molecular microbiology
• Membrane protein structure and function

Background:

• The holin gene 't' in coliphage T4 encodes a protein crucial for initiating phage-induced lysis.
• Coliphage T4 holin has a unique N(in)-C(out) topology with one transmembrane domain, differing from other characterized holins.
• Understanding holin function is key to deciphering phage infection cycles and developing novel antimicrobial strategies.

Purpose of the Study:

• To identify critical residues and domains within the coliphage T4 holin protein essential for its function.
• To investigate the roles of different topological domains in holin-mediated lysis.
• To determine how the T4 antiholin, RI, inhibits holin function and identify domains involved in this interaction.

Main Methods:

• Random mutagenesis was employed to generate a library of lysis-defective coliphage T4 holin alleles.
• Functional assays were performed to assess holin activity and lysis inhibition by antiholin RI.
• Analysis of mutated alleles focused on identifying residues and domains crucial for holin function and RI binding.

Main Results:

• Mutations affecting all three topological domains (N-terminal cytoplasmic, transmembrane, and C-terminal periplasmic) were found to abolish holin function.
• Several lysis-defective mutations within the C-terminal domain impaired the holin's ability to bind the antiholin RI.
• These findings highlight the importance of previously uncharacterized N-terminal and C-terminal domains in lysis and its regulation.

Conclusions:

• The N-terminal, transmembrane, and C-terminal domains of coliphage T4 holin play distinct but essential roles in initiating phage lysis.
• The C-terminal domain is critical for interaction with the antiholin RI, suggesting a regulatory mechanism involving this interaction.
• This study provides new insights into the structure-function relationships of holins and the intricate regulation of phage lysis.