= Operon vs transcription unit
{wiki}
Consider the <E. Coli K-12 MG1655 operon thrLABC>.
That single <operon> can produce two different <mRNA> <transcription units>:
* thrL only, the transcription unit is also called thrL: https://biocyc.org/ECOLI/NEW-IMAGE?object=TU0-42486
* thrL + thrA + thrB + thrC all together, the transcription unit is called thrLABC: https://biocyc.org/ECOLI/NEW-IMAGE?type=OPERON&object=TU00178
The reason for this appears to be that there is a <rho-independent termination> region after thrL. But then under certain conditions, that must get innactivated, and then the thrLABC is produced instead.