The Rhizopus oryzae secreted aspartic proteinase gene family: an analysis of gene expression.
Rhizopus oryzae was shown to possess a secreted aspartic proteinase gene family (sap) of at least four members (sap1-sap4). Within the family there was 77-87% identity at the nucleotide level and 76-92% identity at the amino acid level. Transcription of three members of this gene family (sap1-sap3) required an acidic medium (pH < 4.5) and either nitrogen or sulphur depression. Regulation was co-ordinate and hierarchical, with pH occupying the higher position in the hierarchy. Exogenous protein increased transcript levels, probably via the provision of metabolic intermediates rather than by direct induction of gene expression. sap4 was not expressed under these conditions. SAP1-SAP4 are predicted to have almost identical substrate-binding sites and therefore substrate specificity. It is proposed that sap1-sap3 exist to provide amplified expression of the secreted aspartic proteinase because protein, an important secondary nitrogen source for this fungus, requires extensive degradation to make its nitrogen available to the cell.
Department of Biochemistry, Otago UniversityDunedinNew Zealand.
Peter C
PC
Farley
Institute of Molecular Biosciences, Massey UniversityPrivate Bag 11-222, Palmerston NorthNew Zealand.
Patrick A
PA
Sullivan
D016282:Aspartic Acid Endopeptidases / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D015971:Gene Expression Regulation, Enzymologic; D005800:Genes, Fungal / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D012331:RNA, Fungal / Q000032:analysis; D012335:RNA, Ribosomal / Q000235:genetics; D012233:Rhizopus / Q000201:enzymology* / Q000235:genetics*; D012710:Serum Albumin, Bovine / Q000494:pharmacology / Q000502:physiology
D015345:Oligonucleotide Probes; D012331:RNA, Fungal; D012335:RNA, Ribosomal; D012710:Serum Albumin, Bovine; D016282:Aspartic Acid Endopeptidases