Caufield P W, Shah G R, Hollingshead S K
Department of Oral Biology, School of Dentistry, University of Alabama, Birmingham 35223.
Infect Immun. 1990 Dec;58(12):4126-35. doi: 10.1128/iai.58.12.4126-4135.1990.
Among the attributes thought to contribute to the virulence of Streptococcus mutans is its ability to elaborate bacteriocinlike substances, which may provide a selective force enhancing its colonization potential. One such inhibitory substance, mutacin II, is produced by certain plasmid-containing strains of S. mutans. We introduced insertional mutations into a mutacin II-producing strain of S. mutans (UA96) by transformation with a plasmid carrying Tn916, resulting in transformants bearing single inserts of the transposon at different sites within the chromosome. The insertions identify five different EcoRI fragments required for production of mutacin II (Bac phenotype; bac-1 to bac-5 genotypes). The EcoRI fragments, containing bac-1::Tn916 was ligated into a cosmid vector, pJC74, and transduced into Escherichia coli DH1, where Tn916 is known to be unstable. The loss of Tn916 resulted in a 30-kb plasmid, pPC974, containing approximately 15 kb of S. mutans DNA. A Bac-associated DNA fragment was then subcloned into the streptococcus-E. coli shuttle vector pVA838 and transformed into S. mutants, where it was capable of complementing the bac mutation in the Bac- parent. These findings suggest that we have isolated at least one gene associated with mutacin production.
在被认为有助于变形链球菌毒力的特性中，有一种是它能够产生类细菌素物质，这种物质可能提供一种选择压力，增强其定植潜力。一种这样的抑制性物质，变链菌素II，由某些含有质粒的变形链球菌菌株产生。我们通过用携带Tn916的质粒转化，将插入突变引入到一株产生变链菌素II的变形链球菌（UA96）中，从而得到在染色体不同位点带有转座子单插入的转化体。这些插入确定了产生变链菌素II所需的五个不同的EcoRI片段（Bac表型；bac-1至bac-5基因型）。将含有bac-1::Tn916的EcoRI片段连接到黏粒载体pJC74中，并转导到大肠杆菌DH1中，已知Tn916在该菌中不稳定。Tn916的丢失产生了一个30 kb的质粒pPC974，它含有大约15 kb的变形链球菌DNA。然后将一个与Bac相关的DNA片段亚克隆到链球菌-大肠杆菌穿梭载体pVA838中，并转化到变形链球菌中，在那里它能够互补Bac-亲本中的bac突变。这些发现表明我们已经分离出了至少一个与变链菌素产生相关的基因。
