Chromosome length influences replication-induced topological stress

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA replication generates positive supercoiling ahead of the replication fork.
• Topoisomerases resolve this tension by introducing transient DNA breaks.
• Sister chromatid intertwining occurs as a consequence of fork rotation.

Purpose of the Study:

• To investigate how replication-induced superhelical stress is managed on linear eukaryotic chromosomes.
• To determine the role of chromosome length in handling superhelical tension.
• To elucidate the function of the Smc5/6 complex in mitigating replication stress.

Main Methods:

• Analysis of replication timing in Saccharomyces cerevisiae with varying chromosome lengths.
• Investigating the effects of topoisomerase inhibition on chromosome replication.
• Assessing the chromosomal association of the Smc5/6 complex.
• Evaluating the impact of Smc5/6 complex mutations on DNA intertwining.

Main Results:

• Replication-induced superhelical stress increases with Saccharomyces cerevisiae chromosome length.
• Inhibition of type I topoisomerases causes late replication delays in longer chromosomes.
• The Smc5/6 complex associates more frequently with longer or circularized chromosomes, and upon topoisomerase 2 inactivation.
• Impaired Smc5/6 function leads to increased sister chromatid intertwining.

Conclusions:

• Chromosome length is a critical factor influencing the requirement for superhelical tension release during DNA replication.
• The Smc5/6 complex plays a crucial role in managing replication stress by resolving sister chromatid intertwinings.
• A model is proposed where Smc5/6 facilitates fork rotation by sequestering nascent chromatid intertwinings.