Isolation and characterization of the gene encoding a novel, thermostable serine proteinase from the mould Tritirachium album Limber

A number of proteinases are induced and secreted into the culture medium of Tritirachium album Limber when the nitrogen source is limited to exogenous proteins. We have constructed a cDNA library using the polyadenylated RNA isolated during the nutritional induction with bovine serum albumin. A full-length clone of a gene for a new proteinase (named proteinase R) was identified from this library. This clone contained sequences coding for the 108-amino-acid prepro-leader as well as for the 279-amino-acid mature proteinase. Proteinase R apparently belongs to the subtilisin group of serine proteases that contains disulphide bonds. Homology between proteinase R and proteinase K was found to be about 87% at the nucleotide as well as at the amino acid level. The Brookhaven Protein Data Base co-ordinate file of proteinase K was used as a template to study the proteinase R substitutions in three-dimensional space. The majority of the substitutions of proteinase R with respect to proteinase K were found to be on the exterior of the protein model.