Escherichia coli ribosomal protein L4 stimulates transcription termination at a specific site in the leader of the S10 operon independent of L4-mediated inhibition of translation.

Transcription of the 11-gene S10 operon of Escherichia coli is inhibited by excess ribosomal protein L4, the product of the third gene of the operon. Previous studies suggested that L4 regulates transcription by modulating the level of readthrough at an attenuator in the S10 leader. To understand better the molecular details of the transcriptional regulation, we have determined the site of L4-induced termination of transcription using a method that allows us to map the 5' and 3' ends of newly synthesized RNA. Our results indicate that L4 stimulates termination about 140 bases from the transcription start site. Thus, the termination point is more than 30 bases upstream from the most proximal structural gene of the S10 operon, and coincides with a string of U residues on the descending side of a terminator-like hairpin structure. Since L4 is also known to inhibit translation of the S10 operon, we have analyzed the role of translation control in the protein's regulation of transcription by deleting sequences downstream from the termination site, including bases involved in translation initiation of the proximal structural gene. We find that the first 150 bases of the S10 leader contain the information sufficient for L4-mediated attenuation control and, therefore, that L4 regulates transcription by a mechanisms that is independent of the protein's inhibition of translation.