Y-complex coordinates degradation of ribosomes

Limiting the synthesis and activity of ribosomes is crucial for responding to various stresses, including nutrient starvation or proteotoxic stress. In Bacillus subtilis, this is achieved through the coordinated action of the alarmones (p)ppGpp and the transcription factor Spx. In this study, through a genetic screening for new factors involved in the heat shock response of B. subtilis, we discovered that the Y-complex, which modulates the substrate selection of the endonuclease RNase Y, is important for the heat shock response and the transition to the stationary growth phase. The Y-complex is required for processing different RNAs, including mRNA maturation. Further, we demonstrate that the Y-complex and RNase Y initiate rRNA degradation in mature ribosomes, lowering their abundance. We propose the Y-complex as a system by which B. subtilis regulates protein synthesis and resource allocation at the entry to stationary phase.