Are they with the same notation or not? In RegulonDB, they seemed to be annotated differentially. In a typical operon, some sub-clusters often have alternative transcription start sites or termination sites. In such a case, should the sub-clusters (or sub-operons) be considered as new operons or just new transcription units? I think the original definition of 'operon' should be a cluster of adjacent genes being co-expressed or co-regulated, and a 'transcription unit' should be a cluster of adjacent genes being co-transcribed. Am I right? If I am right, they should be two different subjects; if not, what are the definitions and how to interpret the alternative transcript start/termination sites?