Centromere chromatin may regulate the Flip-flop type of the Mating Type Switching in methylotrophic yeast Ogataea polymorpha

Centromere chromatin has been implicated in silencing the mating type (MAT) locus, which resides within a chromosomal region occupied by OpCse4, the CENP-A homolog, in the Flip-flop type of Mating Type Switching (MTS) in the methylotrophic yeast Ogataea polymorpha. In this study, we investigated the role of centromere chromatin in the recombination event between MAT-adjacent inverted repeats (IRs) that drives MTS. Our results demonstrate that the position of the centromere-proximal IR is critical for efficient recombination between the IRs. Mutants lacking functional OpCse4 or its chaperone OpScm3 exhibit MTS-deficient phenotypes, supporting an active role for centromere chromatin in facilitating MTS. Additionally, we identified OpRad6 and OpBre1 as essential for MTS, and found that deletion of the C-terminal acidic tail of OpRad6 alone is sufficient to disrupt switching. This suggests that monoubiquitylated histone H2B may contribute to MTS either directly or indirectly. Collectively, our findings highlight a direct and functional involvement of centromere chromatin in promoting Flip-flop type MTS in O. polymorpha.