Replication fork remodeling proteins, Smc5/6 and Rtt107, promote palindrome-mediated genome instability

Area of Science:

• Molecular Biology
• Genetics
• Genomics

Background:

• Palindromic DNA sequences are known sources of genomic instability.
• Instability arises from secondary structures like hairpins and cruciforms, cleaved by nucleases.
• Mechanisms of cruciform formation and cleavage in eukaryotes are not fully understood.

Purpose of the Study:

• To elucidate the pathway of secondary structure formation and chromosomal breakage at palindromic sequences.
• To identify the key protein factors involved in palindrome stability.

Main Methods:

• Investigated a pathway involving DNA helicase Mph1, Rad51 recombinase, Rad54 ATPase, Rtt107 scaffold protein, and the Smc5/6 complex.
• Assessed the impact of deleting or mutating these components on double-strand breaks and chromosomal rearrangements at an Alu palindrome.

Main Results:

• Deletion or mutation of any pathway component significantly reduced double-strand breaks at palindromes.
• These genetic alterations also led to a substantial decrease in chromosomal rearrangements.
• Identified a coordinated action of Mph1, Rad51, and Rad54 in generating cruciforms via fork remodeling.
• Showed that Smc5/6 and Rtt107 mark cruciforms for nuclease cleavage.

Conclusions:

• A novel pathway involving Mph1, Rad51, Rad54, Rtt107, and Smc5/6 controls palindrome stability.
• This pathway prevents genomic instability by regulating cruciform formation and cleavage.
• Conserved components suggest these mechanisms are relevant to human diseases linked to palindrome instability.