Comparison ofSchizosaccharomyces pombeexpression systems

Analysis of a variety of problems in yeast relies on ectopic expression of the protein of interest under control of a heterologous promoter. In the fission yeast S.pombe, there are relatively few expression plasmids and most reports of their activity have not been comparative. It is thus difficult to determine the comparability of experiments carried out using different expression vectors. When new promoters are characterised, it is likewise difficult to determine their activity relative to those previously identified. In order to better assess relative promoter strengths, I have compared the activity of several inducible and constitutive expression systems in fission yeast by using a betagalactosidase reporter gene. This allows a more informed choice of appropriate expression systems for analysis of gene function in S.pombe. Four regulatable and two constitutive promoters were compared. Three regulated promoters were derived from the powerful rural promoter, first described by Maundrell (1) and subsequently attenuated with mutations in the TATA box by Basi et al. (2). The other regulated system was constructed from the tetracycline-inducible system described by Faryar and Gatz (3). The two constitutive promoters were the previously described vectors pARTl (containing the adh promoter; .(4) and pSMl (containing the SV40 promoter; 5). The expression vector REP3, containing the thiamine-inducible nmtl promoter (1), and its derivatives REP41 and REP81 (2), which have lower levels of activity due to mutation, all contain an ATG within their polylinker. This was destroyed by insertion of a Xho linker; these derivatives are called REP3X (full strength nmtl), REP41X (slightly weaker; nmtl*) and REP81X (much