Mierau I, Haandrikman A J, Velterop O, Tan P S, Leenhouts K L, Konings W N, Venema G, Kok J
Department of Genetics, University of Groningen, Haren, The Netherlands.
J Bacteriol. 1994 May;176(10):2854-61. doi: 10.1128/jb.176.10.2854-2861.1994.
The gene encoding a tripeptidase (pepT) of Lactococcus lactis subsp. cremoris (formerly subsp. lactis) MG1363 was cloned from a genomic library in pUC19 and subsequently sequenced. The tripeptidase of L. lactis was shown to be homologous to PepT of Salmonella typhimurium with 47.4% identity in the deduced amino acid sequences. L. lactis PepT was enzymatically active in Escherichia coli and allowed growth of a peptidase-negative leucine-auxotrophic E. coli strain by liberation of Leu from a tripeptide. Using a two-step integration-excision system, a pepT-negative mutant of L. lactis was constructed. No differences between the growth of the mutant and that of the wild-type strain in milk or in chemically defined medium with casein as the sole source of essential amino acids were observed.
从pUC19基因组文库中克隆了乳酸乳球菌乳脂亚种（原乳酸亚种）MG1363编码三肽酶（pepT）的基因，并随后进行了测序。乳酸乳球菌的三肽酶与鼠伤寒沙门氏菌的PepT同源，推导的氨基酸序列中有47.4%的同一性。乳酸乳球菌PepT在大肠杆菌中具有酶活性，并通过从三肽中释放亮氨酸使肽酶阴性的亮氨酸营养缺陷型大肠杆菌菌株生长。使用两步整合-切除系统构建了乳酸乳球菌的pepT阴性突变体。在以牛奶或酪蛋白作为必需氨基酸唯一来源的化学限定培养基中，未观察到突变体与野生型菌株生长之间的差异。
