| In budding yeast, phosphoinositide-specific phospholipase C (Plc1p encoded by the PLC1 gene) is the sole source of inositol polyphosphates (InsPs) but deletion of PLC1 is not lethal. However, plc1Delta results in a number of phenotypes, such as slow growth, osmosensitivity, altered cell morphology, and sensitivity to benomyl.;Since it is known that InsPs can regulate transcription through chromatin remodeling complexes, we examined the structure of the SUC2 promoter, both in its repressed and derepressed states, by nucleosome scanning. Expression of SUC2 requires SWI/SNF remodeling of its promoter for induction to occur. Deletion of SWI2 renders the SUC2 promoter unable to undergo remodeling and hence unable to induce expression. The SUC2 promoter in plc1Delta cells is able to undergo remodeling, thus allowing for induction to occur. This fact, coupled with the fact that expression of SER3 and PHO84 are unaltered in plc1Delta cells, as well as the fact that the set of genes with which plc1Delta interacts differs from those of swi2Delta, suggests that InsPs are not general co-factors of chromatin remodeling complexes. Rather, their effects are promoter-specific.;In addition, in this study we found that deletion of PLC1 alters chromatin structure on a global level. The alteration in global chromatin structure is likely to be at least partially due to decreased histone levels. Not only does plc1Delta display decreased levels of histones H3 and H4, but also decreased levels of histone acetylation as acH3 and acH4 levels are low in the mutant. At most of the loci tested by ChIP, we did not detect a dramatic decrease in histone or acetylated histone occupancy, suggesting that the decrease occurs in the soluble pool of histones. The low histone and low acetylation phenotype of plc1Delta can be rescued by deletion of HIR3, as the plc1Deltahir3Delta double mutant has increased protein levels of acH3 and acH4 over the plc1Delta single mutant. Furthermore, the regulation of histone levels occurs at the transcriptional level as plc1Delta cells have decreased histone gene expression, which can also be rescued by deletion of HIR3. However, the mechanism by which PLC1 regulates histone gene expression remains to be determined. |
