Isolation of a novel complex of the SWI/SNF family from Schizosaccharomyces pombe and its effects on in vitro transcription in nucleosome arrays

A snapshot of Snf2 enzymes in fission yeast

Eukaryotic chromatin is remodelled by the evolutionarily conserved Snf2 family of enzymes in an ATP-dependent manner. Several Snf2 enzymes are part of CRCs (chromatin remodelling complexes). In the present review we focus our attention on the functions of Snf2 enzymes and CRCs in fission yeast. We discuss their molecular mechanisms and roles and in regulating gene expression, DNA recombination, euchromatin and heterochromatin structure.

Schizosaccharomyces pombe centromere protein Mis19 links Mis16 and Mis18 to recruit CENP-A through interacting with NMD factors and the SWI/SNF complex

CENP-A is a centromere-specific variant of histone H3 that is required for accurate chromosome segregation. The fission yeast Schizosaccharomyces pombe and mammalian Mis16 and Mis18 form a complex essential for CENP-A recruitment to centromeres. It is unclear, however, how the Mis16-Mis18 complex achieves this function. Here, we identified, by mass spectrometry, novel fission yeast centromere proteins Mis19 and Mis20 that directly interact with Mis16 and Mis18. Like Mis18, Mis19 and Mis20 are localized at the centromeres during interphase, but not in mitosis. Inactivation of Mis19 in a newly isolated temperature-sensitive mutant resulted in CENP-A delocalization and massive chromosome missegregation, whereas Mis20 was dispensable for proper chromosome segregation. Mis19 might be a bridge component for Mis16 and Mis18. We isolated extragenic suppressor mutants for temperature-sensitive mis18 and mis19 mutants and used whole-genome sequencing to determine the mutated sites. We identified two groups of loss-of-function suppressor mutations in non-sense-mediated mRNA decay factors (upf2 and ebs1), and in SWI/SNF chromatin-remodeling components (snf5, snf22 and sol1). Our results suggest that the Mis16-Mis18-Mis19-Mis20 CENP-A-recruiting complex, which is functional in the G1-S phase, may be counteracted by the SWI/SNF chromatin-remodeling complex and non-sense-mediated mRNA decay, which may prevent CENP-A deposition at the centromere.

Fission yeast SWI/SNF and RSC complexes show compositional and functional differences from budding yeast

SWI/SNF chromatin-remodeling complexes have crucial roles in transcription and other chromatin-related processes. The analysis of the two members of this class in Saccharomyces cerevisiae, SWI/SNF and RSC, has heavily contributed to our understanding of these complexes. To understand the in vivo functions of SWI/SNF and RSC in an evolutionarily distant organism, we have characterized these complexes in Schizosaccharomyces pombe. Although core components are conserved between the two yeasts, the compositions of S. pombe SWI/SNF and RSC differ from their S. cerevisiae counterparts and in some ways are more similar to metazoan complexes. Furthermore, several of the conserved proteins, including actin-like proteins, are markedly different between the two yeasts with respect to their requirement for viability. Finally, phenotypic and microarray analyses identified widespread requirements for SWI/SNF and RSC on transcription including strong evidence that SWI/SNF directly represses iron-transport genes.