# Site-to-site mutational dissection of fission yeast cohesin reveals its dynamics

## TL;DR

This study uses fission yeast to understand how mutations in cohesin, a protein complex involved in cell division, affect its function and how other mutations can compensate for these effects.

## Contribution

The study reveals cohesin dynamics through site-specific mutational analysis and suppressor mutation mapping in fission yeast.

## Key findings

- Suppressor mutations in DNA-binding domains of cohesin loader Mis4 or cell-cycle genes can rescue lethality from cohesin ATPase mutations.
- Analogous mutations in Psm1 and Psm3 ATPase domains suggest similar functional roles in cohesin.
- Proper folding of coiled coils and hinge interfaces is critical for cohesin function, as shown by suppressor mutation mapping.

## Abstract

Cohesin is a heteropentameric protein complex that holds sister chromatids together from S phase to anaphase. Its 2 structural maintenance of chromosome subunits form a heterodimer, consisting of an ATPase head domain and a hinge domain connected by long coiled coils. Kleisin subunit associates with the head. Here, using Schizosaccharomyces pombe, we genetically dissected cohesin dynamics based on the relationship between the mutations causing temperature-sensitive and their suppressor mutations. First, we identified suppressor mutations that could rescue the lethality caused by cohesin ATPase mutations. Mutations in the DNA-binding domain of cohesin loader Mis4, or in cell-cycle genes encoding MBF transcription factor complex or Wee1 kinase, rescued both Psm1 and Psm3 ATPase mutants. Then, we performed targeted mutagenesis in both ATPase domains for single-amino-acid substitutions that can rescue the lethality of a kleisin ts mutant at restrictive temperature. Comparison of mutations obtained in Psm1 and Psm3 ATPase domains revealed that analogous mutations in the 2 ATPase domains were frequently observed. Last, suppressors of a coiled-coil mutation were mapped in coiled coils, indicating that proper folding of coiled coils is critical for cohesin functions. Suppressors of a hinge interface mutation are frequently located at the other hinge interface, indicating that the 2 cohesin hinge interfaces work collaboratively in hinge–hinge interactions. Overall, genetic dissection of the relationship between cohesin lethal mutations and their suppressor mutations reflects cohesin dynamics in vivo.