Transcription in Prokaryotes
▪ 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).
Process of transcription in bacteria
▪ The structural genes are monocistronic in eukaryotes.
▪ The process of transcription is similar to that in prokaryotes.
▪ It takes place in the nucleus.
▪ Coding gene sequences called exons form the part of mRNA and non-coding sequence called introns are removed during RNA splicing.
▪ In eukaryotes, three types of RNA polymerases are found in the nucleus:
i. RNA polymerase I transcribes rRNAs (28S, 18S, and 5.8S).
ii. RNA polymerase II transcribes the precursor of mRNA (called heterogeneous nuclear RNA or hnRNA).
iii. RNA polymerase III transcribes tRNA, 5S rRNA and snRNAs (small nuclear RNAs).
