Post-transcriptional regulation of <i>speF</i> expression.

(A) In the absence of orf34 translation, or upon premature translation termination, the transcription termination factor Rho (in blue) binds orf34 RNA, possibly at the CU-rich sequence that precedes the stop codon (blue line) leading to premature transcription termination of orf34-speF operon (T in red). (B) Under conditions of high arginine ribosomes translate orf34 to its stop codon. Pausing at the stop codon prevents the formation of the ‘downstream of stop’ hairpin (DS; blue line) leading to the formation of the alternative structure H in which a ring-like structure is susceptible to degradation and the RBS of speF is inaccessible (C) Under low arginine ribosome attenuation at the consecutive arginine codons enables formation of hairpin DS (in blue), which in turn interferes with the formation of the ring-like structure. Consequently, the long transcript formed under low arginine (structure L) is stable and translationally active.