Regulation of gtf Gene Expression in S mutans

变形链球菌是引起龋齿的病原体。它造成损害的能力与从膳食蔗糖中提取的长链葡萄糖聚合物（葡聚糖）的产生密切相关，这使得细菌拥有表达葡萄糖基转移酶（GTF）的基因家族。变形链球菌中有三种gtf。它们具有50%的序列同一性，由同源的gtfB、gtfC和gtfD基因编码。gtfB和gtfC基因在直接重复序列中发现，编码序列之间仅相隔198个碱基对。尽管gtfB或gtfC的突变都会产生定殖缺陷表型，但对其调控知之甚少。直到最近，唯一已知的调节这些基因的效应物是蔗糖，gtf的底物。补充蔗糖可瞬间诱导gtfB转录融合增加3倍。现在我们已经证明gtfB和gtfC都表现出生长阶段依赖的协调表达。对于这两个基因，表达在指数增长之前达到峰值，并在固定阶段早期下降超过100倍。在本提案中，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，并通过诱变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，因此需要根据细菌的致病机制对这里发现的遗传因素进行检查。

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.