Hemmings B A, Zubenko G S, Hasilik A, Jones E W
Proc Natl Acad Sci U S A. 1981 Jan;78(1):435-9. doi: 10.1073/pnas.78.1.435.
Carboxypeptidase Y, a vacuolar enzyme in Saccharomyces cerevisiae, is synthesized as a larger precursor whose apparent molecular mass is approximately 67,000 daltons. We have characterized a recessive mutation, pep4-3, that prevents maturation of this precursor. The accumulated precursor does not possess enzymatic activity. We have shown that the precursor accumulating in the pep4-3 mutant is not produced in a doubly mutant strain that also bears a mutation in the carboxypeptidase Y structural gene that eliminates production of carboxypeptidase Y. We have also shown that a nonsense fragment of carboxypeptidase Y is processed. Although there is evidence that proteinase B can catalyze the conversion of the precursor to a mature form in vitro, nonsense mutations in the structural gene for proteinase B, PRB1, do not affect the levels of carboxypeptidase Y activity, and strains bearing these mutations produce a carboxypeptidase Y of apparently normal size. Hence, proteinase B is not essential for the maturation of carboxypeptidase Y precursor in vivo. The pep4-3 mutation affects at least five vacuolar enzymes. This suggests that there is a processing event common to all of these enzymes.
羧肽酶Y是酿酒酵母中的一种液泡酶，它以一种表观分子量约为67,000道尔顿的更大前体形式合成。我们鉴定了一种隐性突变pep4 - 3，它阻止了这种前体的成熟。积累的前体不具有酶活性。我们已经表明，在pep4 - 3突变体中积累的前体在一个双突变菌株中不产生，该双突变菌株的羧肽酶Y结构基因也有一个突变，消除了羧肽酶Y的产生。我们还表明羧肽酶Y的一个无义片段被加工。虽然有证据表明蛋白酶B在体外可以催化前体转化为成熟形式，但蛋白酶B结构基因PRB1中的无义突变并不影响羧肽酶Y的活性水平，携带这些突变的菌株产生的羧肽酶Y大小明显正常。因此，蛋白酶B对于体内羧肽酶Y前体的成熟不是必需的。pep4 - 3突变影响至少五种液泡酶。这表明所有这些酶存在一个共同的加工事件。
