An amber mutation in a ribosomal protein gene: ineffective suppression stimulates operon-specific transcription.

The effects of inefficient suppression and the accompanying polarity of an amber mutation in the ribosomal protein gene rplC (L3) on the transcriptional activities of several ribosomal protein operons were investigated. The L3 gene is proximally located in the S10 operon. Inefficient suppression of the mutation specifically stimulated transcription of regions both proximal and distal to the site of mutation by about twofold. In contrast, no effect on the transcriptional activity of regions within the alpha and spc ribosomal protein operons was observed. Thus, transcription of the S10 operon could be actively and specifically regulated in response to a deficiency in one or more of the protein products from the operon. We presume that this transcriptional control acts at the level of transcription initiation, but we cannot exclude the possibility of some other unknown transcriptional regulatory mechanism.