Final answer:
The first step of termination for RNA polymerase II in prokaryotes involves encountering specific termination signals, which can lead to rho-dependent or rho-independent termination modes. Rho-dependent termination relies on the rho protein causing dissociation of RNA from DNA. Rho-independent termination is mediated by a hairpin structure in the RNA causing the polymerase to stall and release the transcript.
Step-by-step explanation:
The first step of termination for RNA polymerase II, which is a RNA polymerase enzyme found in eukaryotic cells, involves encountering specific termination signals on the DNA template.
These are nucleotide sequences that signal the enzyme to stop transcription and release the newly synthesized RNA molecule. In prokaryotes, the termination can be either rho-dependent or rho-independent.
In rho-dependent termination, as the polymerase nears the end of the transcription unit, it transcribes a region rich in cytosine residues.
The rho protein, an ATP-dependent helicase, binds to the RNA and moves toward the RNA polymerase.
When it collides with the stalled polymerase, it induces the separation of the RNA transcript from the DNA template.
The rho-independent mechanism involves a hairpin structure formed by the RNA transcript, which leads to the stalling of the RNA polymerase and eventual dissociation of the enzyme from the DNA template and the RNA transcript.