The Mechanism Exploration Of Heterochromatin Spreading At Mating Type Locus In Fission Yeast

In eukaryote cells, heterochromatin is highly decorated, existing in a condensed state. Heterochromatin is inactive in DNA metabolic activities and has the feature of spreading out on cis in a stochastic manner, inducing gene silencing in neighboring region. A kind of DNA sequence called boundary elements can constrain such spreading. In fission yeast, mating type locus is one of the main heterochromatin domains. There is a 230bp boundary element, termed REII, locating at the centromere-proximal side of mat2-P at mating type locus. REII can attract the spreading of heterochromatin and ensure the silence of mating type locus together with other pathways. The mechanism by which REII performs the function remains unknown. Here, we identified functionally important nine-nucleotide DNA segments—R box and R-like box within REII. Mutation of R box diminishes the effect of REII nearly entirely in attracting heterochromatin spreading. And the synergistic effect of R box and R-like box enable REII performs its intact function in attracting heterochromatin spreading and silencing genes. On the other hand, DNA pull-down affinity purification and mass spectrum analysis identified RNA Pol Ⅲ proteins as REII binding factors in vitro. These proteins may play a role in the progress of REII attracting heterochromatin spreading and remaining heterochromatin structure at mating type locus.