A群鏈球菌是常見的致病菌，它可以引起很廣泛的人類疾病。目前在A群鏈球菌中已知有許多總體性的調控因子參與致病機轉的調控，如 mga, rgg, covR 等…。然而，在毒力因子的調控網中還存在許多的爭議與未知的調控機制，如 Srv 便是一種 CRP/FNR 家族的轉錄調控因子，參與A群鏈球菌複雜的調控網路。本研究主要針對Srv探討它如何影響下游基因。由北方墨點法、西方墨點法、SpeB 活性試驗或冷光 speB 啟動子活性試驗都證明 Srv 是 speB 的負向調控因子。SpeB 是一種半胱胺酸蛋白水解，在A群鏈球菌感染中扮演重要的毒力因子。然而，先前的研究發現高量表現 SpeB 的 srv 突變株在小鼠感染模式中毒力顯著下降，這表示可能還有其他毒力因子被 Srv 所調控。為了搜尋有哪些毒力因子可能被 Srv 調控，本研究在A群鏈球菌全基因體序列中搜尋預測的 Srv 結合序列，發現在 mga 與 slo 基因的上游有 Srv 的結合序列，而 Mga 已知是一個重要的調控因子，它可以正向調控 M protein (emm) 與 C5a peptidase (scpA)。由 RT-PCR、北方墨點法及real time RT-PCR 顯示在 srv 突變株中 mga、emm、scpA、slo 表現量有部分下降，且在互補株中恢復。冷光 mga 啟動子活性試驗也顯示 srv 突變株中的 mga 活性低於野生株約兩倍。此外，由 real time RT-PCR 與西方墨點法的分析發現 Srv 於 log phase 高量表現，此表現型態與 mga 相符。在 srv 突變株中也發現 SLO 溶血素活性降低，利用人類全血殺菌試驗證實突變株的相對抗殺菌能力也低於野生株約 80%。這些研究結果顯示 Srv 對於A群鏈球菌在血液中的存活扮演很重要的角色，它不僅可以藉由調控 mga 來抵抗殺菌效果，而且也調控 slo 來逃脫吞噬作用。

Group A streptococcus (GAS) is a common pathogen that can cause a wide-spectrum of human diseases. Several global regulators have been extensively studied in GAS such as mga, rgg, covR etc. However, there still have a lot of controversy and unknown mechanisms that are involved in virulence regulation. Srv is a Crp/Fnr family transcriptional regulator and involved in a complex regulatory network of GAS. The aim of this study was to understand how Srv affected the downstream genes. The northern blot, western blot, SpeB activity assay and luciferase speB promoter assay all showed Srv is a negative regulator of speB, Streptococcal pyrogenic exotoxin B, a cysteine proteinase, which plays an important role in GAS infection. However, the highly expressed speB in a srv mutant strain showed low virulence in mice model reported previously, suggesting some other virulence factors may be involved. In order to find out which virulence factors can be regulated by Srv, the putative Srv binding box in GAS whole genome was searched. Two genes, mga and slo had the Srv putative binding box. Mga is an important global regulator, which has shown a regulation of M protein (emm) and C5a peptidase (scpA). RT-PCR, Northern blot and real time RT-PCR showed mga, emm, scpA, and slo decreased expression in srv mutant, and restored in a complementary strain. Luciferase assay also showed that the mga activity in srv mutant was two times lower than that of wild-type strain. In addition, Srv showed a highly expression in log phase by real time RT-PCR and western blot which is correlated with the expression pattern of mga. SLO hemolysin activity decreased in the srv mutant. The human whole blood killing assay was also confirmed that the relative resistant to bactericidal effect was 80% decrease in mutant. Based on these results suggest that Srv plays an important role in blood survival, it not only positively regulate mga to resistant the bactericidal effect but also regulate streptolysin O to evade phagocytosis.

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