Labrie Steve, Vukov Natasa, Loessner Martin J, Moineau Sylvain
Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Que., Canada G1K 7P4.
FEMS Microbiol Lett. 2004 Apr 1;233(1):37-43. doi: 10.1016/j.femsle.2004.01.038.
The bacteriophage lysis cassette, which comprises a lysin and a holin gene, was analyzed in 18 Lactococcus lactis phages. A muramidase motif was found in the lysins of c2-like phages, while an amidase motif was observed in the lysins of 936-like phages. Both amidase and muramidase types were detected among the P335 phages. The P335 lysins were separated into three groups based on amino acid sequence identity. A class I holin was recognized in 936-like and c2-like phages, whereas P335-like phages possess class II holins. The P335 holins were further divided into four groups based on sequence identity. Only the holins of 936-like phages contained putative dual-start motifs. The unusual lysis cassette of the highly virulent P335-like phage ul36 contains a unique holin (orf74B) upstream of a lysin which is present in several other P335-like phages. Using the lambdadelta Sthf system, we demonstrated that gpORF74B induces cell lysis at the same time as lambdadelta Sthf::S105, the effector of lambda lysis. Transcriptional analysis of ul36 lysis cassette showed that first transcripts are detected 35 min after infection of L. lactis cells. The lysis clock of phage ul36 appears to be controlled by the late expression of the holin and lysin genes.
对包含溶菌酶和穿孔素基因的噬菌体裂解盒在18株乳酸乳球菌噬菌体中进行了分析。在c2样噬菌体的溶菌酶中发现了一种胞壁质酶基序，而在936样噬菌体的溶菌酶中观察到一种酰胺酶基序。在P335噬菌体中检测到了酰胺酶和胞壁质酶两种类型。根据氨基酸序列同一性，P335溶菌酶被分为三组。在936样和c2样噬菌体中识别出I类穿孔素，而P335样噬菌体拥有II类穿孔素。根据序列同一性，P335穿孔素进一步分为四组。只有936样噬菌体的穿孔素含有推定的双起始基序。高毒力的P335样噬菌体ul36的异常裂解盒在溶菌酶上游含有一个独特的穿孔素（orf74B），该溶菌酶存在于其他几种P335样噬菌体中。使用λδSthf系统，我们证明gpORF74B与λ裂解效应物λδSthf::S105同时诱导细胞裂解。对ul36裂解盒的转录分析表明，在乳酸乳球菌细胞感染后35分钟检测到第一批转录本。噬菌体ul36的裂解时钟似乎受穿孔素和溶菌酶基因的晚期表达控制。
