Role of conserved sequence elements in yeast centromere DNA.

Conserved sequence features in Saccharomyces cerevisiae CEN DNA are confined to a region of approximately 120 bp. The highly conserved 8 bp at the left (PuTCACPuTG) constitute the left boundary of a functional CEN DNA as shown by the analysis of a series of Bal31 deletions. The right boundary of a functional CEN DNA lies within the conserved 25 bp at the right (TGT-T-TG--TTCCGAA-----AAA) or a few base pairs further outside of the 120-bp region. One mutant which just lacks the left conserved DNA element PuTCACPuTG can still assemble into a partially functional mitotic centromere and it assembles into a well functioning meiotic centromere. The sequences between the two conserved terminal DNA elements can be increased in length (+50%) or in GC content (from 6% to 12%) without measurable changes in mitotic and meiotic segregations of plasmids carrying such CEN mutations. The naturally occurring length and GC content of this centromere DNA sequence element is, therefore, not essential for centromere function. We discuss the possibility that it partly acts as a hinge region between two domains. Finally, we tested integrations of CEN DNA into the genome and found a toleration of wild-type CEN6 DNA when present 3' of the LYS2 gene.