The role of chromatin structure in control of the function of DNA in transcription, replication, recombination and repair has become increasingly obvious. To study this area, we use a highly tractable system, Saccharomyces cerevisiae , which offers the potential for genetic manipulation of both the gene under examination and the background genotypes for proteins of interest. The ability to place a gene on a minichromosome and isolate that structure, as native chromatin, in various functional states, offers an unprecedented opportunity to relate composition, structure and function of chromatin. Our studies focus on genes regulated by the mating type locus.
Yeast exist in two mating types, a and .
In addition to its promoter, the entire coding sequence of the STE6 gene is packaged as precisely positioned nucleosomes. Genetic evidence implicated several other proteins in repression of -cell specific genes. We have now shown that, in addition to Mcm1p, and the 2 repressor, the amino terminal regions of histone H4 and the products of the SSN6 and TUP1 genes are required to organize chromatin on -cell specific genes. We find an absolute concordance of the presence of the organized chromatin structure with complete repression of -cell specific promoters. This chromatin structure suggests a model for larger repressed domains such as the silent mating type loci, telomeres and centromeres.