Transcription start sites and processing sites of the A3(2) operon have been investigated by a combination of and transcription analyses. The data from these approaches are consistent with the existence of four transcription sites, corresponding to the promoters P1-P4. The transcription start sites are located at −597, −416, −334 and −254 relative to the start of the 16S rRNA gene. Two putative processing sites were identified, one of which is similar to a sequence reported earlier in and other eubacteria. The P1 promoter is likely to be recognized by the RNA polymerase holoenzyme containing σ, the principal sigma factor in P2 also shares homology with the consensus for vegetative promoters, but has a sequence overlapping the consensus −35 region that is also present in the −35 regions of P3 and P4. The −35 sequence common to P2, P3 and P4 is not similar to any other known consensus promoter sequence. In fast-growing mycelium, P2 appears to be the most frequently used promoter. Transcription from all of the promoters decreased during the transition from exponential to stationary phase, although transcription from P1 and P2 ceased several hours before that from P3 and P4.


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