Kita K, Suisha M, Kotani H, Yanase H, Kato N
Department of Biotechnology, Tottori University, Japan.
Nucleic Acids Res. 1992 Aug 25;20(16):4167-72. doi: 10.1093/nar/20.16.4167.
StsI endonuclease (R.StsI), a type IIs restriction endonuclease found in Streptococcus sanguis 54, recognizes the same sequence as FokI but cleaves at different positions. A DNA fragment that carried the genes for R.StsI and StsI methylase (M.StsI) was cloned from the chromosomal DNA of S.sanguis 54, and its nucleotide sequence was analyzed. The endonuclease gene was 1,806 bp long, corresponding to a protein of 602 amino acid residues (M(r) = 68,388), and the methylase gene was 1,959 bp long, corresponding to a protein of 653 amino acid residues (M(r) = 76,064). The assignment of the endonuclease gene was confirmed by analysis of the N-terminal amino acid sequence. Genes for the two proteins were in a tail-to-tail orientation, separated by a 131-nucleotide intercistronic region. The predicted amino acid sequences between the StsI system and the FokI system showed a 49% identity between the methylases and a 30% identity between the endonucleases. The sequence comparison of M.StsI with various methylases showed that the N-terminal half of M.StsI matches M.NIaIII, and the C-terminal half matches adenine methylases that recognize GATC and GATATC.
StsI核酸内切酶（R.StsI）是在血链球菌54中发现的一种IIs型限制性核酸内切酶，它识别的序列与FokI相同，但切割位置不同。从血链球菌54的染色体DNA中克隆了携带R.StsI基因和StsI甲基化酶（M.StsI）的DNA片段，并对其核苷酸序列进行了分析。核酸内切酶基因长1806 bp，对应于一个602个氨基酸残基的蛋白质（M(r)=68388），甲基化酶基因长1959 bp，对应于一个653个氨基酸残基的蛋白质（M(r)=76064）。通过对N端氨基酸序列的分析证实了核酸内切酶基因的归属。这两种蛋白质的基因呈尾对尾方向排列，由一个131个核苷酸的基因间区域隔开。StsI系统和FokI系统之间预测的氨基酸序列显示，甲基化酶之间的同一性为49%，核酸内切酶之间的同一性为30%。M.StsI与各种甲基化酶的序列比较表明，M.StsI的N端一半与M.NIaIII匹配，C端一半与识别GATC和GATATC的腺嘌呤甲基化酶匹配。
