When Ribonucleases Come into Play in Pathogens: A Survey of Gram-Positive Bacteria

Figure 2

Diagram illustrating different mechanisms of posttranscriptional regulation. (a) Stabilization of S. pyogenes ska mRNA. Transcript levels of ska are regulated by RNase-mediated decay. Under stress conditions, the FasX sRNA is expressed and binds to the 5′ leader region of ska mRNA inhibiting RNase degradation [70]. (b) S. aureus RNAIII/RNase III repression of translation. The quorum-sensing regulatory RNAIII uses a regulatory hairpin to bind to spa mRNA (or SA1000) target sequence. The initial loop-loop interaction is converted to a duplex sequestering the Shine-Dalgarno sequence (SD). Access of the ribosome is blocked and translation is repressed. RNase III is recruited to the hybrid region and to an additional hairpin present in spa and cleaves the transcript making the regulatory event irreversible [71, 72]. (c) Repression of B. subtilis TxpA toxin synthesis. The asRNA Rat is transcribed convergently and is fully complementary to the txpA mRNA. Binding of Rat asRNA to txpA transcript induces rapid degradation of the mRNA [73]. The RNase performing the initial cleavage might be RNase III although the nature of the enzyme and the structure of the hybrid are not yet determined.