Quantitative aspects of the use of bacterial chloramphenicol acetyltransferase as a reporter system in the yeast Saccharomyces cerevisiae

An improved chloramphenicol acetyltransferase assay for Plasmodium falciparum transfection

Chloramphenicol acetyltransferase (CAT) is a popular choice as a reporter gene in transgenic studies in many different organisms, including Plasmodium falciparum. For experimental investigations into transfection efficiency and gene expression a robustly quantitative assay is of great value. On investigation the published protocol for CAT assay of P. falciparum was found to be prone to saturation due to the long incubation time; moreover, cellular material extracted from the parasite increased the enzyme activity. A new protocol was developed which is quantitative across a range of three orders of magnitude of CAT activity, takes account of the cellular extract effect, and is more rapid than the established method. The value of these improvements was demonstrated by analysing the effects of parasitaemia and amount of plasmid on transfection efficiency with both old and new methods.

Rap1p-binding sites in the saccharomyces cerevisiae GPD1 promoter are involved in its response to NaCl

Mechanisms involved in transcriptional regulation of the osmotically controlled GPD1 gene in Saccharomyces cerevisiae were investigated by promoter analysis. The GPD1 gene encodes NAD(+)-dependent glycerol-3-phosphate dehydrogenase, a key enzyme in the production of the compatible solute glycerol. By analysis of promoter deletions, we identified a region at nucleotides -478 to -324, in relation to start of translation, to be of great importance for both basal activity and osmotic induction of GPD1. Electrophoretic mobility shift and DNase I footprint analyses demonstrated protein binding to parts of this region that contain three consensus sequences for Rap1p (repressor activator protein 1)-binding sites. Actual binding of Rap1p to this region was confirmed by demonstrating enhanced electrophoretic mobility of the protein-DNA complex with extracts containing an N-terminally truncated version of Rap1p. The detected Rap1p-DNA interactions were not affected by changes in the osmolarity of the growth medium. Specific inactivation of the Rap1p-binding sites by a C-to-A point mutation in the core of the consensus showed that this factor is a major determinant of GPD1 expression since mutations in all three putative binding sites for Rap1p strongly hampered osmotic induction and drastically lowered basal activity. We also show that the Rap1p-binding sites appear functionally distinct; the most distal site (core of the consensus at position -386) exhibited the highest affinity for Rap1p and was strictly required for low salt induction (< or =0.6 m NaCl), but not for the response at higher salinities (> or =0.8 m NaCl). This indicates tha different molecular mechanisms might be operational for low and high salt responses of the GPD1 promoter.