García P, Alonso J C, Suárez J E
Instituto Universitario de Biotecnología de Asturias, Facultad de Medicina, Universidad de Oviedo, Spain.
Mol Microbiol. 1997 Feb;23(3):505-14. doi: 10.1046/j.1365-2958.1997.d01-1863.x.
The terminal nucleotide sequence of the Lactobacillus casei bacteriophage A2 DNA revealed a single-stranded extension 13 bases in length (5'-AACGGTCGGCCTC-3') at its 3' termini that defines the packaging initiation nicking site (cosN). The cosN sequence is bisected by an axis of hyphenated twofold rotational symmetry. Directly and inverted repeated sequences located to the left (cosL) and the right (cosR) of the cosN site were observed. Analysis of the 3.4 kb EcoRI DNA sequence surrounding the cos region revealed four complete and one incomplete open reading frames (orfs). Northern blots indicated that all were cotranscribed in a single mRNA molecule in excess of 10 kb that appeared late during infection. Minicell studies indicated that the four orfs were translated into protein. From the ORF3 amino acid sequence DNA-binding and NTP-binding domains can be predicted. The purified ORF3 (predicted molecular mass 16.8 kDa) shows specific binding to the A2 cos region, so it was renamed gp3. Gp3 forms a specific complex with a 369 bp cos DNA segment in the presence of ATP. Gp3 interaction with the intrinsically bent cos DNA segment induces intramolecular ligation in the presence of T4 DNA ligase. The data presented here suggest that gp3 is the small subunit of the terminase enzyme.
干酪乳杆菌噬菌体A2 DNA的末端核苷酸序列显示，其3'末端有一个长度为13个碱基的单链延伸（5'-AACGGTCGGCCTC-3'），该延伸定义了包装起始切口位点（cosN）。cosN序列被一个间断的二重旋转对称轴平分。在cosN位点的左侧（cosL）和右侧（cosR）观察到了正向和反向重复序列。对cos区域周围3.4 kb的EcoRI DNA序列分析揭示了四个完整的和一个不完整的开放阅读框（orf）。Northern印迹表明，所有这些开放阅读框都在一个超过10 kb的单一mRNA分子中共同转录，该mRNA在感染后期出现。小细胞研究表明，这四个开放阅读框被翻译成蛋白质。从ORF3氨基酸序列可以预测出DNA结合和NTP结合结构域。纯化的ORF3（预测分子量为16.8 kDa）显示出与A2 cos区域的特异性结合，因此将其重新命名为gp3。在ATP存在的情况下，gp3与一个369 bp的cos DNA片段形成特异性复合物。在T4 DNA连接酶存在的情况下，gp3与固有弯曲的cos DNA片段的相互作用诱导分子内连接。此处提供的数据表明，gp3是末端酶的小亚基。
