Regulation of gtf Gene Expression in S mutans

变形链球菌是一种引起龋齿的病原体。它造成损害的能力与来自饮食蔗糖的长链葡萄糖聚合物(葡聚糖)的产生密切相关，这使得细菌拥有一系列表达酶的基因，称为葡萄糖基转移酶(GTF)。变形链球菌中有三种GTF。它们有50%的序列同源性，由同源的gtfb、gtfc和gtfD基因编码。Gtfb和gtfc基因以直接重复的形式存在，编码序列之间只有198个碱基对的间隔。虽然gtfb或gtfc的突变产生了一种定植缺陷的表型，但人们对它们的调控知之甚少。直到最近，唯一已知的调节这些基因的效应物是蔗糖，它是GTFS的底物。添加蔗糖瞬间诱导GTFB转录融合增加3倍。现在我们已经证明了GTFB和GTFc都表现出协同生长阶段依赖的表达。对于这两个基因，表达在指数增长之前达到峰值，在早期稳定期下降超过100倍。在这项建议中，我们打算进一步研究这一现象，包括鉴定关键的顺式和反式作用元件，并通过突变来确定这些元件如何影响GTF基因的表达。由于这些GTF基因参与了定植过程，因此需要从细菌的致病机制方面检查这里发现的遗传因素。

Streptococcus mutans is a causative agent of dental caries. It's ability to inflict damage is strongly linked to the production of long chain glucose polymers (glucans) derived from dietary sucrose which allow the bacteria possesses a family of genes that express enzymes called glucosyltransferases (GTF). There are three GTFs in S. mutans. They share 50 percent sequence identity and are encoded by the homologous gtfB, gtfC and gtfD genes. The gtfB and gtfC gene are found in direct repeat with a mere 198 base paries separation between coding sequences. Although mutations in either gtfB or gtfC produce a colonizing deficient phenotype, little is known about their regulation. Until recently, the only effector known to regulate these genes was sucrose, the substrate of the GTFs. Supplemented sucrose transiently induces a 3-fold increase in a gtfB transcriptional fusion. Now we have demonstrated that both gtfB and gtfC show coordinated growth phase- dependent expression. For both genes, expression peaks prior to exponential growth and falls over 100-fold by early stationary phase. In this proposal, we intend to further study this phenomenon including identifying critical cis and trans acting elements and through mutagenesis determine how these elements affect gtf gene expression. Since these gtf genes are involved in the colonization process, the genetic elements that are found here will need to be examined in terms of the bacteria's pathogenic mechanisms.