Used in Positive-strand RNA virus to replicate.
I don't think it's present outside viruses. Well regulated organisms just transcribe more DNA instead.
A single operon may produce multiple different transcription units depending on certain conditions, see: operon vs transcription unit.
For an example, see E. Coli K-12 MG1655 operon thrLABC.
Multiple different transcription units can be produced by a single operon, see: operon vs transcription unit.
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: biocyc.org/ECOLI/NEW-IMAGE?object=TU0-42486
- thrL + thrA + thrB + thrC all together, the transcription unit is called thrLABC: 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.
Multiple genes coding for multiple proteins in one transcription unit, e.g. e. Coli K-12 MG1655 gene thrL and e. Coli K-12 MG1655 gene thrA are both prat of the E. Coli K-12 MG1655 operon thrLABC.
Articles by others on the same topic
Transcription is the biological process through which the information encoded in a gene's DNA is copied into messenger RNA (mRNA). This is the first step in gene expression, leading to the synthesis of proteins. Here's a brief overview of the transcription process: 1. **Initiation**: The transcription process begins when the enzyme RNA polymerase binds to a specific region of the DNA called the promoter, which is located near the start of a gene.