McShan W M, Tang Y F, Ferretti J J
Department of Microbiology and Immunology, BMSB, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA.
Mol Microbiol. 1997 Feb;23(4):719-28. doi: 10.1046/j.1365-2958.1997.2591616.x.
The region of temperate bacteriophage T12 responsible for integration into the chromosome of Streptococcus pyogenes has been identified. The integrase gene (int) and the phage attachment site (attP) are found immediately upstream of the gene for speA, the latter of which is known to be responsible for the production of erythrogenic toxin A (also known as pyrogenic exotoxin A). The integrase gene has a coding capacity for a protein of 41457 Da, and the C-terminus of the deduced protein is similar to other conserved C-terminal regions typical of phage integrases. Upstream of int is a second open reading frame, which is capable of encoding an acidic protein of 72 amino acids (8744 Da); the position of this region in relation to int suggests it to be the phage excisionase gene (xis). The arms flanking the integrated prophage (attL and attR) were identified, allowing determination of the sequences of the phage (attP) and bacterial (attB) attachment sites. A fragment containing the integrase gene and attP was cloned into a streptococcal suicide vector; when introduced into S. pyogenes by electrotransformation, this plasmid stably integrated into the bacterial chromosome at attB. The insertion site for the phage into the S. pyogenes chromosome was found to be in the anticodon loop of a putative type II gene for a serine tRNA. attP and attB share a region of identity that is 96 bp in length; this region of identity corresponds to the 3' end of the tRNA gene such that the coding sequence remains intact after integration of the prophage. The symmetry of the core region of att may set this region apart from previously described phage attachment sites (Campbell, 1992), and may play a role in the biology of this medically important bacteriophage.
已确定温和噬菌体T12整合到化脓性链球菌染色体中的区域。整合酶基因（int）和噬菌体附着位点（attP）位于speA基因的紧邻上游，后者已知负责产生致热外毒素A（也称为化脓性外毒素A）。整合酶基因编码一种41457 Da的蛋白质，推导蛋白质的C末端与噬菌体整合酶典型的其他保守C末端区域相似。int上游是第二个开放阅读框，能够编码一种72个氨基酸（8744 Da）的酸性蛋白质；该区域相对于int的位置表明它是噬菌体切除酶基因（xis）。确定了整合原噬菌体两侧的臂（attL和attR），从而确定了噬菌体（attP）和细菌（attB）附着位点的序列。将包含整合酶基因和attP的片段克隆到链球菌自杀载体中；通过电转化将该质粒导入化脓性链球菌时，它在attB处稳定整合到细菌染色体中。发现噬菌体插入化脓性链球菌染色体的位点位于丝氨酸tRNA假定的II型基因的反密码子环中。attP和attB共享一个96 bp长的同源区域；该同源区域对应于tRNA基因的3'末端，使得原噬菌体整合后编码序列保持完整。att核心区域的对称性可能使该区域与先前描述的噬菌体附着位点不同（坎贝尔，1992），并且可能在这种医学上重要的噬菌体的生物学特性中发挥作用。
