Large palindromes in the lambda phage genome are preserved in a rec+ host by inhibiting lambda DNA replication

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Phage lambda carrying large palindromes hinders growth in rec+ Escherichia coli.
• Palindromes are unstable in recBC sbcB strains, leading to deletions and overgrowth by modified phage.

Purpose of the Study:

• To investigate the stability and recovery of large palindromic sequences in phage lambda DNA during infection.
• To understand the role of DNA replication and host factors in palindrome stability.

Main Methods:

• Preparation of phage lambda stocks with large palindromes (2 X 4200 base pairs).
• Infection of rec+ Escherichia coli hosts with replication-blocked phage.
• Analysis of phage DNA recovery in unreplicated chromosomes.

Main Results:

• Large (2 X 4200 bp) and smaller (2 X 265 bp) palindromes are recovered intact in unreplicated chromosomes of rec+ hosts.
• Phage growth is inhibited by large palindromes in rec+ E. coli but not in recBC sbcB strains.

Conclusions:

• DNA replication appears to drive the extrusion of palindromic sequences in vivo.
• Extruded palindromes form secondary structures that are substrates for recBC and sbcB gene products.
• This mechanism may explain palindrome instability and deletion formation in certain E. coli strains.