Luan Shi-Lu, Granlund Margareta, Norgren Mari
Department of Biomedical Laboratory Science, Umeå University, S-901 87, Umeå, Sweden.
Gene. 2003 Jul 17;312:305-12. doi: 10.1016/s0378-1119(03)00634-6.
The group II intron (GBSi1) identified downstream of the C5a-peptidase gene (scpB) in a subpopulation of Streptococcus agalactiae isolates is a suggested marker for a separate genetic lineage of serotype III isolates. In the present study two additional copies of GBSi1, one of which not previously described, were identified among serotype III isolates. All intron copies shared a common target site motif. A single copy of GBSi1 was found in a subgroup of serotype II and V isolates. In these isolates, the intron had inserted downstream of scpB, which suggests that this is the primary insertion site for GBSi1. Most bacterial group II introns described to date reside in transposable elements. The scpB locus was found to be flanked by insertion sequences similar to what has been described in an intronless serotype Ia isolate. However, this region contained an additional 2.1 kb DNA fragment present only in intron carrying isolates. This DNA fragment contained a partial transposase and putative plasmid related proteins. This may suggest that GBSi1 once was brought into the S. agalactiae genome by an integrated plasmid.
在无乳链球菌分离株亚群中，C5a肽酶基因（scpB）下游鉴定出的II组内含子（GBSi1）被认为是III型分离株一个独立遗传谱系的标记。在本研究中，在III型分离株中鉴定出另外两个GBSi1拷贝，其中一个是此前未描述过的。所有内含子拷贝都共享一个共同的靶位点基序。在II型和V型分离株的一个亚组中发现了一个GBSi1拷贝。在这些分离株中，内含子插入到了scpB下游，这表明这是GBSi1的主要插入位点。迄今为止描述的大多数细菌II组内含子都存在于转座元件中。发现scpB基因座两侧是与无内含子Ia型分离株中所描述的类似的插入序列。然而，该区域包含一个仅存在于携带内含子的分离株中的额外2.1 kb DNA片段。该DNA片段包含一个部分转座酶和假定的质粒相关蛋白。这可能表明GBSi1曾经是通过整合质粒进入无乳链球菌基因组的。
