Chromosomal inheritance of epigenetic states in fission yeast during mitosis and meiosis.

Inheritance of the active and inactive states of gene expression by individual cells is crucial for development. In fission yeast, mating-type region consists of three loci called mat1, mat2, and mat3. Transcriptionally silent mat2 and mat3 loci are separated by a 15 kb interval, designated the K-region, and serve as donors of information for transcriptionally active mat1 interconversion. In a strain carrying replacement of 7.5 kb of the K-region with the ura4 gene, we discovered that ura4 silencing and efficiency of mating-type switching were covariegated and were regulated by an epigenetic mechanism. Genetic analyses demonstrated that epigenetic states were remarkably stable not only in mitosis but also in meiosis and were linked to the mating-type region. This study indicates that different epigenetic states are heritable forms of chromatin organization at the mat region.