Watson R J, Wheatcroft R
Plant Research Centre, Agriculture Canada, Ottawa, Ontario.
DNA Seq. 1991;2(3):163-72. doi: 10.3109/10425179109039686.
Nucleotide sequencing of Rhizobium meliloti insertion sequence ISRm1 showed that it is 1319 nucleotides long and includes 32/31 nucleotide terminal inverted repeats. Analysis of five different insertion sites using sequencing primers complementary to sequences within the left and right ends demonstrated that ISRm1 generates five bp direct repeats at the sites of insertion. Although ISRm1 has shown a target preference for certain short regions (hot spots), there was no apparent similarity in the DNA sequences near the insertion sites. On one strand ISRm1 contains two contiguous open reading frames (ORFs) spanning most of its length. ISRm1 was found to have over 50% sequence homology to insertion sequences IS2 from Escherichia coli and IS426 from Agrobacterium tumefaciens. Their sizes, the sequences of their inverted repeats, and the characteristics of their insertion sites are also comparable, indicating that ISRm1, IS2 and IS426 belong to a class of related insertion sequences. Comparison of the proteins potentially encoded by these insertion sequences showed that the two ORFs found in ISRm1 are also present in IS2 and IS426, suggesting that they may be functional genes.
苜蓿根瘤菌插入序列ISRm1的核苷酸测序表明，它长1319个核苷酸，包含32/31个核苷酸的末端反向重复序列。使用与左右末端序列互补的测序引物对五个不同插入位点进行分析，结果表明ISRm1在插入位点产生5个碱基对的正向重复序列。尽管ISRm1对某些短区域（热点）表现出靶标偏好，但插入位点附近的DNA序列没有明显的相似性。在一条链上，ISRm1包含两个连续的开放阅读框（ORF），覆盖其大部分长度。发现ISRm1与大肠杆菌的插入序列IS2和根癌农杆菌的IS426具有超过50%的序列同源性。它们的大小、反向重复序列的序列以及插入位点的特征也具有可比性，表明ISRm1、IS2和IS426属于一类相关的插入序列。对这些插入序列可能编码的蛋白质进行比较，结果表明在ISRm1中发现的两个ORF也存在于IS2和IS426中，这表明它们可能是功能基因。
