Transcription in Prokaryotes 

▪ In prokaryotes, the structural gene is polycistronic and continuous. 

▪ In bacteria, the transcription of all the three types of RNA (mRNA, tRNA and rRNA) is catalysed by single DNA-dependent enzyme, called the RNA polymerase. 

▪ In E. coli bacterium, the RNA polymerase has co-factors β, β′, α, α′ and ω along with σ (sigma) factor, to catalyse the process. 

▪ The transcription is completed in three steps: initiation, elongation and termination. 

▪ Initiation: σ (sigma) factor recognises the start signal and promotor region on DNA which then along with RNA polymerase binds to the promoter to initiate transcription. 

▪ Elongation: The RNA polymerase after initiation of RNA transcription loses the σ factor but continues the polymerisation of ribonucleotides to form RNA. 

▪ Termination: Once the RNA polymerase reaches the termination region of DNA, the RNA polymerase is separated from DNA–RNA hybrid, as a result nascent RNA separates. This process is called termination which is facilitated by a termination factor ρ (rho). 

▪ In prokaryotes, mRNA does not require any processing, so both transcription and translation occur in the cytosol. It can be said that transcription and translation are coupled together.