Yeast Genetics and Molecular Biology 1996
Madison, Wisconsin
August 1996


Name: Brewster, Neil K
Mailing Address: Sir Charles Tupper Bldg., Halifax, NS B3H 4H7 Nova Scotia Canada
Email Address: nbrewste@is.dal.ca
Phone and Fax numbers: 902-494-3883, 902-494-1355

Positive and negative regulation of transcription by the Cdc68 protein.

N. K. Brewster, 1 G. C. Johnston, 2 and R. A. Singer, 1. 1) Dept. Biochemistry, Dalhousie Univ., Halifax, N.S., Canada B3H 4H7; (902)494-3883, 2) Dalhousie Univ.

Genetic studies show that the Cdc68/Spt16 protein is a global yeast gene activator. A cdc68 mutation inhibits gene expression and alters transcription initiation at promoters harboring *delta*-element insertions (spt- phenotype). cdc68 mutations also allow expression of core promoters lacking UASs. At a genetic level, therefore, Cdc68 activates and represses gene expression. Altered histone gene expression, and resultant changes in histone stoichiometry, can also derepress core promoters and exert an spt- phenotype through effects on chromatin structure. A cdc68 mutation affects expression from the HTA1-HTB1 locus that encodes histones H2A and H2B, raising the possibility that repression of core promoters is a reflection of Cdc68 effects on histone expression. To test this we measured mRNA abundance in cdc68 mutant cells under conditions that preclude histone gene expression. We found that core-promoter derepression in cdc68 mutant cells, as least for the suc2*delta*UAS test promoter, can occur without altered histone gene expression. Thus Cdc68 may have a relatively direct role in chromatin-mediated repression at core promoters. These observations are consistent with our findings that Cdc68 N-terminal sequences are necessary for core-promoter repression but dispensable for gene activation and essential functions of Cdc68.