Martínez-Abarca F, Toro N
Grupo de Ecología Genética, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Profesor Albareda 1, 18008 Granada, Spain.
Nucleic Acids Res. 2000 Nov 1;28(21):4397-402. doi: 10.1093/nar/28.21.4397.
RmInt1 is a group II intron of Sinorhizobium meliloti which was initially found within the insertion sequence ISRm2011-2. Although the RmInt1 intron-encoded protein lacks a recognizable endonuclease domain, it is able to mediate insertion of RmInt1 at an intron-specific location in intronless ISRm2011-2 recipient DNA, a phenomenon termed homing. Here we have characterized three additional insertion sites of RmInt1 in the genome of S.meliloti. Two of these sites are within IS elements closely related to ISRm2011-2, which appear to form a characteristic group within the IS630-Tc1 family. The third site is in the oxi1 gene, which encodes a putative oxide reductase. The newly identified integration sites contain conserved intron-binding site (IBS1 and IBS2) and delta' sequences (14 bp). The RNA of the intron-containing oxi1 gene is able to splice and the oxi1 site is a DNA target for RmInt1 transposition in vivo. Ectopic transposition of RmInt1 into the oxi1 gene occurs at 20-fold lower efficiency than into the homing site (ISRm2011-2) and is independent of the major RecA recombination pathway. The possibility that transposition of RmInt1 to the oxi1 site occurs by reverse splicing into DNA is discussed.
RmInt1是苜蓿中华根瘤菌的一个II类内含子，最初发现于插入序列ISRm2011-2中。尽管RmInt1内含子编码的蛋白质缺乏可识别的内切酶结构域，但它能够介导RmInt1插入无内含子的ISRm2011-2受体DNA的内含子特异性位点，这一现象称为归巢。在此，我们鉴定了苜蓿中华根瘤菌基因组中RmInt1的另外三个插入位点。其中两个位点位于与ISRm2011-2密切相关的IS元件内，它们似乎在IS630-Tc1家族中形成一个特征性群体。第三个位点位于oxi1基因中，该基因编码一种假定的氧化还原酶。新鉴定的整合位点包含保守的内含子结合位点（IBS1和IBS2）和δ'序列（14 bp）。含内含子的oxi1基因的RNA能够剪接，并且oxi1位点是RmInt1在体内转座的DNA靶点。RmInt1异位转座到oxi1基因的效率比转座到归巢位点（ISRm2011-2）低20倍，并且独立于主要的RecA重组途径。我们讨论了RmInt1转座到oxi1位点是通过反向剪接进入DNA的可能性。
