Molecular Analysis of RT-like gene which is newly found in Escherichia coli.

来自多种生物体的许多遗传元件已被证明含有开放阅读框架，其编码的蛋白质序列与逆转录病毒逆转录酶相似。我们从大肠杆菌K-12中分离到一个新的逆转录酶(RT)样基因，该基因位于大肠杆菌遗传图谱上的6min。该基因编码一个由322个氨基酸组成的蛋白质，它具有在所有类似RT的序列中都可以识别的保守结构域I到VII。在保守结构域VII的下游，发现了IS5插入元件。氨基酸序列比对表明，该类RT蛋白属于真菌II类丝裂软骨内含子中的RTS，而不是肠道细菌中与msDNA相关的RTS。该基因在具有多拷贝的E.ColiC和志贺氏菌I型菌株中也存在，但在E.coliB和所研究的其他细菌种中不存在。其中一个来源于E.coliC的RT-基因被克隆和测序。它编码479个氨基酸。在E.coliC中的类RT蛋白大于在E.ColiK-12中的类RT蛋白。两个RT-1~322的氨基酸序列完全相同。在保守的RT结构域的下游，我们发现了629插入元件，该元件被认为来自宋内氏志贺菌。有趣的是，我们在RT基因末端密码子和IS629之间发现了与酿酒酵母有丝分裂细胞色素氧化酶内含子2同源的45bp长序列。

Many genetic elements from a wide variety of organisms have been shown to contain open-reading frames encoding proteins that are similar sequence to retroviral reverse transcriptases. We isolated a new reverse transcriptase (RT) -like gene from Escherichia coli K-12 and it is located at 6 min on the E.coli genetic map. The gene encodes a protein that consists of 322 amino acids, which has conserved domains I to VII that could be identified in all RT-like sequences. Downstream from the conserved domain VII,IS 5 insertion element was found. Amino acid alignment of the RT-like proteins and various kinds of RTs shows that the RT-like protein belongs to rather the RTs found in certain fungal group II mitochondorial introns than the msDNA related RTs found in enteric bacteria. The gene also exists in E.coli C with multicopy and Shigella dysenteriae type I strain, but dose not exist in E.coli B and othe bacterial species investigated. One of the RT-genes derived from E.coli C was cloned and sequenced. It encodes 479 amino acides. RT-like protein in E.coli C is larger than RT-like protein in E.coli K-12. The amino acid sequences from 1 to 322 of both RTs are the same. Downstream of the conserved RT domains, we found IS 629 insertion element which is thought to be derived from Shigella sonnei. Interestingly we found 45 bp long sequence homologous to mitochondorial cytochrome oxidase intron2 of Saccharomyces cerevisiae between terminal codon of RT gene and IS 629.