A feedback loop coupling 5 S rRNA synthesis to accumulation of a ribosomalprotein

We have shown that elevated expression of ribosomal protein L5 in Xenopus e mbryos results in the ectopic activation of 5 S rRNA genes that are normall y inactive. This transcriptional stimulation mimics the effect of overexpre ssing transcription factor IIIA (TFIIIA), the 5 S rRNA gene-specific transc ription factor. The results support a model in which a network of nucleic a cid-protein interactions involving 5 S rRNA, the 5 S rRNA gene, TFIIIA, and L5 mediates both feedback inhibition of 5 S rRNA synthesis and coupling of 5 S rRNA synthesis to accumulation of a ribosomal protein, L5. We propose that these mechanisms contribute to the homeostatic control of ribosome ass embly.