Negative regulator of sigma-B activity. Non-phosphorylated RsbS binds to RsbT, preventing its association with RsbU. Requires any one of RsbRA, RsbRB, RsbRC or RsbRD to sequester RsbT. When RsbS and the RsbR paralog(s) are phosphorylated, they release RsbT, which can then bind and activate RsbU. Interacts with RsbRA, RsbRB in the stressosome. The stressosome probably also contains RsbRC and RsbRD. Phosphorylated by RsbT. Dephosphorylated by RsbX.