The absence of the Isw2p-Itc1p chromatin-remodelling complex induces mating type-specific and Flo11p-independent invasive growth of Saccharomyces cerevisiae.

The Isw2p-Itc1p chromatin remodelling complex of Saccharomyces cerevisiae is a member of the ISWI class of ATPases with a nucleosome spacing activity, involved in regulation of expression of a broad spectrum of genes. Its absence causes derepression of a-specific genes and aberrant morphology in alpha-mating type cells. We report here that the deletion of the ISW2 gene in the originally non-invasive BY strain induces mating type-specific invasive growth strongly affected by nitrogen starvation. Although the Flo11 protein was postulated to be critical for haploid invasive growth, we showed that the invasive growth caused by the isw2 and itc1 deletions in alpha-mating type cells was Flo11p-independent. This type of invasive growth was proved to be a consequence of the activation of the pheromone response pathway. Our results suggest that Isw2 and Itc1 proteins do not have the same impact on the described phenomenon.

Development of a reporter system for the yeast Schwanniomyces occidentalis: influence of DNA composition and codon usage.

In this paper we report on searching for suitable reporters to monitor gene expression and protein secretion in the amylolytic yeast Schwanniomyces occidentalis. Several potential reporter and marker genes, formerly shown to be functional in other yeasts, were cloned downstream from the homologous invertase gene (INV) promoter and their activity was followed in conditions of repression and derepression of the INV promoter. However, neither beta-glucuronidase nor beta-lactamase nor phleomycin resistance-conferring gene, all originating from E. coli, were expressed in S. occidentalis cells to such a level to allow for monitoring of their activity. All the reporter genes tested have a higher percentage of GC (47-62%) in their DNA compared to the DNA composition of S. occidentalis genes that are more AT-rich (36% GC). The codon usage of all the reporter genes also varies from that of 16 so far sequenced S. occidentalis genes. This suggests that an appropriate composition of DNA and a codon usage similar to S. occidentalis genes might be very important parameters for an efficient expression of a heterologous gene in Schwanniomyces occidentalis. Indeed, two genes originating from Staphylococcus aureus, with an AT-content in their DNA similar to that of S. occidentalis, were functionally expressed in S. occidentalis cells. Both a phleomycin resistance-conferring gene and a chloramphenicol acetyltransferase-encoding gene thus represent suitable reporters of gene expression and protein secretion in S. occidentalis. Additionally, we show in this work that the transcription-regulating region and the signal peptide sequence of the S. occidentalis invertase gene were efficient to direct gene expression and subsequent protein secretion in Saccharomyces cerevisiae.