Aminopeptidase yspI was purified to apparent homogeneity from the fission yeast Schizosaccharomyces pombe. The molecular mass of the native enzyme was estimated to be 184 kDa by gel filtration chromatography. A value of 92 kDa was calculated after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme is thus a dimer with two identical subunits. Optimum pH for cleavage of synthetic aminoacyl-4-nitroanilides is 7.0. Mercury ions, EDTA and chloroquine were found to be potent inhibitors of aminopeptidase yspI activity. Substrate specificity studies indicate that the purified enzyme cleaves L-lysine-4-nitroanilide with high efficiency.

The structural gene, APEl, (LAP4), for the vacuolar aminopeptidase I of Saccharomyces cerevisiae was cloned with the aid of a staining technique which permitted monitoring of aminopeptidase activity in yeast colonies. Genetic linkage data demonstrate that integrated copies of the cloned gene map to the APE1 locus. The nucleotide sequence of the cloned gene was determined. The open reading frame of APE1 consists of 514 codons and, therefore, encodes a larger protein (MW 57 003) than the reported mature aminopeptidase ysc1 (MW 44 SOO), suggesting that proteolytic processing must occur. A 1.75-kb mRNA, which is made in substantial amounts only when yeast cells have exhausted the glucose supply, was identified.

Plasmids capable of complementing lupl, lap2 and lap3 mutations [R. J. Trumbly and G. Bradley (1983) J. Bucteriol. 156, [36][37][38][39][40][41][42][43][44][45][46][47][48] were isolated from a yeast YEpl3 library by screening for activity against the chromogenic aminopeptidase substrate L-leucine P-naphthylamide in intact yeast colonies. The genomic inserts were shown to contain the structural genes for aminopeptidases yscII, yscIII and ysclV. Plasinids containing the gene encoding aminopeptidase yscII of Sacchuromyce.y cerevisiae, APE2 (LAPI) were analyzed in detail. APE2 was determined by DNA blot analysis to be a singlecopy gene located on chromosome XI. The cloned fragment was used to identify a 2.7-kb mRNA. The proteolytic system of the yeast Succhuromyces cerrvihiue has attracted considerable attention and is still actively studied (for reviews, see [I, 21). The yeast proteinases located in the vacuole, the lysosome-like organelle [3], are by far the best characterized. The genes encoding proteinase yscA, proteinase yscB, aminopeptidase yscI, dipeptidyl aminopeptidase yscV, carboxypeptidase yscY and carboxypeptidase yscS have been cloned and sequenced [4-221 and their biosynthesis and sorting have been examined (reviewed in [13]).Matile et al. [14] detected four aminopeptidases with activity on leucine /3-naphthylamide after separating crude extracts from yeast by starch gel electrophoresis. Four aminopeptidases capable of hydrolyzing tripeptides were deCorrespondeelwe to P. SuCrez-Rendueles,

Expression of the vacuolar carboxypeptidase S (CPS1) gene in Saccharomyces cerevisiae is regulated by the availability of nutrients. Enzyme production is sensitive to nitrogen catabolite repression; i.e. the presence of ammonium ions maintains expression of the gene at a low level. Transfer of ammonium-glucose pre-grown cells to a medium deprived of nitrogen causes a drastic increase in CPS1 RNA level provided that a readily usable carbon source, such as glucose or fructose, is available to the cells. Derepression of the gene by nitrogen limitation is cycloheximide-insensitive. Neither glycerol, ethanol, acetate nor galactose support derepression of CPS1 expression under nitrogen starvation conditions. Non-metabolizable sugar analogs (2-deoxyglucose, 6-methyl-glucose or glucosamine) do not allow derepression of CPS1, showing that the process is energy-dependent. Production of carboxypeptidase yscS also increases several-fold when ammonium-pregrown cells are transferred to media containing glucose and a non-readily metabolizable nitrogen source such as proline, leucine, valine or leucyl-glycine. Analysis of CPS1 expression in RAS2+ (high cAMP) and ras2 mutant (low cAMP) strains and in cells grown at low temperature (23 degrees C) and in heat-shocked cells (38 degrees C) shows that steady-state levels of CPS1 mRNA are not controlled by a low cAMP level-signalling pathway.

No abstract