YEAST CALMODULIN AND A CONSERVED NUCLEAR-PROTEIN PARTICIPATE IN THE INVIVO BINDING OF A MATRIX ASSOCIATION REGION

Chromatin becomes reorganized during mitosis each cell cycle. To ident ify genes potentially involved in these supramolecular events, we have used a colony-color assay to screen temperature-sensitive mutants of Saccharomyces cerevisiae. When a sequence that mediates attachment to the nuclear matrix in vitro was inserted into the GAL1 promoter of a l acZ fusion gene, beta-galactosidase synthesis was inhibited. This obse rvation permitted screening for temperature-sensitive-inducible mutant s on 5-bromo-4-chloro-3-indolyl beta-D-galactoside plates. Only 1 of 2 0 complementation groups of newly isolated mutants exhibited temperatu re-sensitive inducibility for the matrix association region but not fo r control CEN3 or STE6 inserts-a cmd1 mutant in which the last 7 amino acids of calmodulin were truncated by an ochre termination codon. Ano ther mutant (smi1) exhibited a rare phenotype at the nonpermissive con dition, which included S phase and budding arrest. We cloned and seque nced the SMI1 gene, which encodes a 57-kDa polypeptide with evolutiona rily conserved epitope(s) found in mammalian cell nuclei. Thus, we pro vide evidence for involvement of calmodulin and another conserved prot ein in the in vivo binding of a matrix association region.