Oscarsson Jan, Kanth Anna, Tegmark-Wisell Karin, Arvidson Staffan
Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, S-17177 Stockholm, Sweden.
J Bacteriol. 2006 Dec;188(24):8526-33. doi: 10.1128/JB.00866-06. Epub 2006 Sep 29.
In most Staphylococcus aureus strains, inactivation of sarA increases hla transcription, indicating that sarA is a repressor. However, in S. aureus NCTC 8325 and its derivatives, used for most studies of hla regulation, inactivation of sarA resulted in decreased hla transcription. The disparate phenotype of strain NCTC 8325 seems to be associated with its rsbU mutation, which leads to sigma(B) deficiency. This has now been verified by the demonstration that sarA repressed hla transcription in an rsbU+ derivative of strain 8325-4 (SH1000). That sarA could act as a repressor of hla in an 8325-4 background was confirmed by the observation that inactivation of sarA in an agr sarS rot triple mutant dramatically increased hla transcription to wild-type levels. However, the apparent role of sarA as an activator of hla in 8325-4 was not a result of the rsbU mutation alone, as inactivation of sarA in another rsbU mutant, strain V8, led to increased hla transcription. Northern blot analysis revealed much higher levels of sarS mRNA in strain V8 than in 8325-4, which was likely due to the mutation in the sarS activator, tcaR, in 8325-4, which was not found in strain V8. On the other hand, the relative increase in sarS transcription upon the inactivation of sarA was 15-fold higher in 8325-4 than in strain V8. Because of this, inactivation of sarA in 8325-4 means a net increase in repressor activity, whereas in strain V8, inactivation of sarA means a net decrease in repressor activity and, therefore, enhanced hla transcription.
在大多数金黄色葡萄球菌菌株中，sarA的失活会增加hla的转录，这表明sarA是一种阻遏物。然而，在用于大多数hla调控研究的金黄色葡萄球菌NCTC 8325及其衍生物中，sarA的失活导致hla转录减少。菌株NCTC 8325的不同表型似乎与其rsbU突变有关，该突变导致σ(B)缺乏。现在这一点已通过以下证明得到证实：sarA在菌株8325-4（SH1000）的rsbU+衍生物中抑制hla转录。agr sarS rot三重突变体中sarA的失活使hla转录显著增加至野生型水平，这一观察结果证实了sarA在8325-4背景下可作为hla的阻遏物。然而，sarA在8325-4中作为hla激活剂的明显作用并非仅由rsbU突变导致，因为另一个rsbU突变体V8菌株中sarA的失活也导致hla转录增加。Northern印迹分析显示，V8菌株中sarS mRNA的水平比8325-4中的高得多，这可能是由于8325-4中sarS激活剂tcaR的突变，而V8菌株中未发现该突变。另一方面，sarA失活后sarS转录的相对增加在8325-4中比在V8菌株中高15倍。因此，8325-4中sarA的失活意味着阻遏物活性的净增加，而在V8菌株中，sarA的失活意味着阻遏物活性的净减少，从而增强了hla转录。
