THE YEAST GAL11 PROTEIN IS INVOLVED IN REGULATION OF THE STRUCTURE AND THE POSITION EFFECT OF TELOMERES

GAL11 is an auxiliary transcription factor that functions either positively or negatively, depending on the structure of the target promoters and the combination of DNA-bound activators. In this report, we demonstrate that a gal11 Delta mutation caused a decrease in the length of the telomere C(1-3)A tract, a derepression of URA3 when it is placed next to telomere, and an increase in accessibility of the telomeric region to dam methylase, indicating that GAL11 is involved in the regulation of the structure and the position effect of telomeres. The defective position effect in a gal11 Delta strain was suppressed by overproduction of SIR3, whereas overexpression of GAL11 failed to restore the telomere position effect in a sir3 Delta strain. Hyperproduced GAL11 could partially suppress the defect in silencing at HMR in a sir1 Delta mutant but not that in a sir3 Delta mutant, suggesting that GAL11 can replace SIR1 function partly in the silencing of HMR. Overproduced SIR3 also could restore silencing at HMR in sir1 Delta cells. In contrast, SIR1 in a multicopy plasmid relieved the telomere position effect, especially in a gal11 Delta mutant. Since chromatin structure is thought to play a major role in the silencing at both the HM loci and telomeres, GAL11 is likely to participate in the regional regulation of transcription by modulating the chromatin structure.