Chromosomal boundaries in S. cerevisiae.

Chromatin boundary elements or insulators in metazoans delimit distinct chromosomal domains of gene expression. Recently, DNA sequences with properties similar to boundary elements were also discovered in Saccharomyces cerevisiae. These sequences block the spread of transcriptionally silent chromatin, the yeast equivalent of metazoan heterochromatin, and are referred to as 'heterochromatin barriers'. These barriers share no sequence homology but all consist of multiple binding sites for various regulatory proteins. Current data suggest that barriers may function in yeast by recruiting a protein complex that precludes nucleosome assembly and thereby disrupts a contiguous array of nucleosomes required for the spread of silent chromatin.