Alvarez M A, Herrero M, Suárez J E
Area de Microbiología, Universidad de Oviedo, Oviedo, E-33006, Spain.
Virology. 1998 Oct 10;250(1):185-93. doi: 10.1006/viro.1998.9353.
The region of the bacteriophage A2 genome involved in site-specific recombination with the DNA of Lactobacillus spp. has been identified. Two orfs, transcribed from the same strand, have been found immediately upstream of the phage attachment site (attP). The orf adjacent to attP predicts a 385-amino-acid protein that presents significant similarity with site-specific recombinases of the integrase family. The other orf encodes a basic polypeptide of 76 amino acid residues. The junctions of the prophage with the genomes of its hosts have been determined, allowing the identification of the host attachment site (attB), which has a common 19-nucleotide core region with attP. The attB site is located at the 3' end of the transfer RNALeu gene (anticodon CAA). Nonreplicative plasmids containing the A2-specific recombination cassette integrate into different lactobacilli but also into unrelated Gram-positive bacteria such as Lactococcus lactis and even into Escherichia coli. In Lc. lactis, integration occurs in a previously unknown intergenic region, whereas in E. coli, it maps within the rrnD operon, 5' of rrsD gene. Comparison of the integration sites in the different hosts indicates that some flexibility is permitted in the attB sequence, since Lc. lactis and E. coli only share 13 and 11 nucleotides, respectively, with the 19-nucleotide core sequence of the lactobacilli.
已确定噬菌体A2基因组中与乳酸杆菌属DNA进行位点特异性重组的区域。在噬菌体附着位点（attP）上游紧邻处发现了两个从同一条链转录的开放阅读框（orf）。与attP相邻的orf预测编码一种385个氨基酸的蛋白质，该蛋白质与整合酶家族的位点特异性重组酶具有显著相似性。另一个orf编码一个由76个氨基酸残基组成的碱性多肽。已确定原噬菌体与其宿主基因组的连接点，从而得以鉴定宿主附着位点（attB），它与attP有一个共同的19个核苷酸的核心区域。attB位点位于亮氨酰转运RNA基因（反密码子CAA）的3'端。含有A2特异性重组盒的非复制性质粒可整合到不同的乳酸杆菌中，也可整合到无关的革兰氏阳性菌如乳酸乳球菌中，甚至可整合到大肠杆菌中。在乳酸乳球菌中，整合发生在一个以前未知的基因间区域，而在大肠杆菌中，它定位在rrnD操纵子内，rrsD基因的5'端。不同宿主中整合位点的比较表明，attB序列允许一定程度的灵活性，因为乳酸乳球菌和大肠杆菌与乳酸杆菌的19个核苷酸核心序列分别仅共享13和11个核苷酸。
