A single gene (tts) located outside the cap locus directs the formation of Streptococcus pneumoniae type 37 capsular polysaccharide. Type 37 pneumococci are natural, genetically binary strains.
A single gene (tts) located outside the cap locus directs the formation of Streptococcus pneumoniae type 37 capsular polysaccharide. Type 37 pneumococci are natural, genetically binary strains.
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DOI：
10.1084/jem.190.2.241
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发表时间：
1999-07-19
影响因子：
15.3
通讯作者：
Garcia, E
中科院分区：
文献类型：
--
作者：
Llull, D;Munoz, R;Lopez, R;Garcia, E
研究了37型肺炎球菌荚膜生物合成的分子机制。37型肺炎球菌荚膜生物合成是一种由槐糖基单元（β-d-Glc-（1→2）-β-d-Glc）通过β-1，3键连接而成的同多糖。值得注意的是，37型荚膜的生物合成是由一个单一的基因（tts）驱动的，该基因位于远离负责荚膜形成的cap基因座，在迄今为止在肺炎链球菌中表征的所有类型中。然而，在37型菌株中发现了与cap 33 f簇几乎相同的cap 37基因座，尽管其一些基因因突变而失活。tts基因已被测序并确定了其转录起始点。Tts显示纤维素酶和其他β-糖基转移酶的特征序列基序。将tts基因插入肺炎球菌DNA中会引起明显的基因组重组，在37型临床分离株中，染色体中通常相隔350 kb以上的基因会被定位在一起。用tts转化属于10种不同血清型（或血清群）的包囊肺炎球菌菌株，合成37型多糖，导致形成显示二元型荚膜的菌株。37型肺炎球菌构成了第一例自然的、遗传上的二元菌株，并代表了一种新型的替代型间转化机制。
The molecular aspects of the type 37 pneumococcal capsular biosynthesis, a homopolysaccharide composed of sophorosyl units (β-d-Glc-(1→2)-β-d-Glc) linked by β-1,3 bonds, have been studied. Remarkably, the biosynthesis of the type 37 capsule is driven by a single gene (tts) located far apart from the cap locus responsible for capsular formation in all of the types characterized to date in Streptococcus pneumoniae. However, a cap37 locus virtually identical to the cap33f cluster has been found in type 37 strains, although some of its genes are inactivated by mutations. The tts gene has been sequenced and its transcription start point determined. Tts shows sequence motifs characteristic of cellulose synthases and other β-glycosyltransferases. Insertion of the tts gene into the pneumococcal DNA causes a noticeable genome reorganization in such a way that genes normally separated by more than 350 kb in the chromosome are located together in clinical isolates of type 37. Encapsulated pneumococcal strains belonging to 10 different serotypes (or serogroups) transformed with tts synthesized type 37 polysaccharide, leading to the formation of strains that display the binary type of capsule. Type 37 pneumococcus constitutes the first case of a natural, genetically binary strain and represents a novel alternative to the mechanisms of intertype transformation.