Regulation of proteinase activity in Aspergillus nidulans.

1976) which is a defective in killer toxin secretion and in secretion of mature a-factor (T. Achstetter & D. H. Wolf, unpublished work). With the aid of the two model substrates, Cbz-Tyr-Lys and Cbz-Tyr-Lys-Arg, we also found carboxypeptidase activity in the membrane fraction, which is able to remove the two amino acids lysine and arginine and may thus be involved in further processing of the a-factor molecule. The enzyme was named carboxypeptidase ysca (T. Achstetter & D. H. Wolf, unpublished work). Another proteolytic process is involved in the biogenesis of the vacuole, the lysosome-like cell compartment of yeast. Carboxypeptidase yscY (Hasilik & Tanner, 1978) and the two endoproteinases yscA and yscB (Mechler et al., 1982) were found to be synthesized as precursor molecules of M , 67000, 52000 and 42000 respectively, which undergo proteolytic processing to yield their mature forms of M , 61 000, 42000 and 33000 respectively. The function of the putative processing proteinase most likely resides in the activation of the enzymes. Proteinase yscB had been proposed to be the processing enzyme for the carboxypeptidase yscY precursor (Hasilik & Tanner, 1978). However, studies on mutants lacking proteinase yscB ruled out this possibility (Wolf & Ehmann, 1979; Hemmings et al., 1981). No new candidate proteinase for the processing process has yet been found. Table 2 summarizes our present knowledge on the yeast proteinases and their functions. Large gaps concerning their function still exist. It is not hard to guess that the number of proteinases presented in Table 2 will most likely increase when more studies are done.