Identification of Schizosaccharomyces pombe transcription factor PGA4, which binds cooperatively to Saccharomyces cerevisiae GAL4-binding sites

Hsp90 inhibitors and drug resistance in cancer: the potential benefits of combination therapies of Hsp90 inhibitors and other anti-cancer drugs

Hsp90 is a chaperone protein that interacts with client proteins that are known to be in the cell cycle, signaling and chromatin-remodeling pathways. Hsp90 inhibitors act additively or synergistically with many other drugs in the treatment of both solid tumors and leukemias in murine tumor models and humans. Hsp90 inhibitors potentiate the actions of anti-cancer drugs that target Hsp90 client proteins, including trastuzumab (Herceptin™) which targets Her2/Erb2B, as Hsp90 inhibition elicits the drug effects in cancer cell lines that are otherwise resistant to the drug. A phase II study of the Hsp90 inhibitor 17-AAG and trastuzumab showed that this combination therapy has anticancer activity in patients with HER2-positive metastatic breast cancer progressing on trastuzumab. In this review, we discuss the results of Hsp90 inhibitors in combination with trastuzumab and other cancer drugs. We also discuss recent results from yeast focused on the genetics of drug resistance when Hsp90 is inhibited and the implications that this might have in understanding the effects of genetic variation in treating cancer in humans.

In vitro transcription and start site selection in Schizosaccharomyces pombe

We have used the fission yeast Schizosaccharomyces pombe to establish both a biochemical and genetic system to study the roles of general transcription factors in transcription initiation. Extracts were prepared that faithfully transcribed S. pombe promoters and the results confirm that, in contrast to the budding yeast Saccharomyces cerevisiae, in vitro transcription in S. pombe initiates near to the TATA element. S. pombe transcription relies on upstream activation sequence elements and these can be replaced successfully with sites for binding Gal4-VP16 activators. Although it is mammalian-like in these respects, S. pombe initiation uses an unusual scanning mechanism. This directs initiation, preferentially using purines, within a narrow window approximately 25-40 base-pairs downstream from the edge of the TATA element. Genetic experiments showed that this scanning mechanism was associated with the properties of the TFIIB polypeptide. When human TFIIB was expressed in S. pombe, it was accepted by the endogenous transcription machinery and caused initiation to be restricted to the closer edge of this window, corresponding to the distance in humans. Preliminary experiments suggested that S. cerevisiae TFIIB was not accepted. The results enlarge the potential for using fission yeast to study the properties of general transcription factors such as TFIIB in choosing the sites at which transcription initiates.

A rapid permeabilization procedure for accurate quantitative determination of beta-galactosidase activity in yeast cells

A procedure is described which allows the rapid permeabilization of yeast cells, Schizosaccharomyces pombe and Saccharomyces cerevisiae, for quantitative in situ assays of beta-galactosidase activity. Yeast cells are permeabilized by incubation in buffer containing 0.2% of the detergent sodium lauroyl sarcosinate without any need for washing or vortexing. This procedure is equally applicable to fresh and frozen samples. It is compared to earlier reported methods and found to be superior by being more accurate and less time-consuming.