i. Role of polymerase in transcription in bacteria
a. Initiation: σ (sigma) factor recognises the start signal and promotor region on DNA and the σ (sigma) with RNA polymerase binds to the promoter and initiates transcription.
b. Elongation: The RNA polymerase after initiation of RNA transcription loses the σ-factor but continues the process of RNA formation.
c. 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 certain termination factor .
Role of polymerase in transcription in eukaryotes
a. In eukaryotes, apart from the RNA polymerase found in the organelles, three types of RNA polymerases are found in the nucleus.
b. RNA polymerase II transcribes the precursor of mRNA (called as heterogeneous nuclear RNA (hnRNA).
c. RNA polymerase III helps in transcription of tRNA, 5S rRNA, and snRNAs (small nuclear RNAs).
ii. Francis Crick postulated the role of an adaptor. tRNA or transfer RNA is the adaptor molecule.
