Define transcription termination in bacteria vs eukaryotes.

• A. Bacteria terminate via intrinsic (hairpin with/without rho) mechanisms; eukaryotes terminate after cleavage and polyadenylation of the pre-mRNA and RNA polymerase II release.
• B. Bacteria terminate via intrinsic hairpin formation; eukaryotes terminate after RNA polymerase II release.
• C. Both terminate after RNA polymerase II release.
• D. Bacteria terminate through cleavage and polyadenylation of pre-mRNA.

Answer: (A)

Transcription termination in bacteria vs eukaryotes reflects two different ways the cell ends RNA synthesis and hands off the transcript.

In bacteria, termination can happen in two main ways. The intrinsic or rho-independent route uses a nascent RNA hairpin structure formed by a GC-rich inverted repeat, followed by a string of uracils. This hairpin destabilizes the transcription complex and causes RNA polymerase to dissociate, ending transcription. The rho-dependent route uses a separate helicase, Rho, which binds the RNA and catches up to the paused polymerase, pulling the transcript away and terminating transcription.

In eukaryotes, termination of RNA polymerase II transcripts is tied to RNA processing. After the pre-mRNA is cleaved at the polyadenylation signal, the mature mRNA is released and a poly(A) tail is added. This processing step, along with subsequent release of RNA polymerase II (sometimes aided by exonucleases), ends transcription.

So the best description is that bacteria terminate via intrinsic hairpin structures (with or without Rho) and eukaryotes terminate after cleavage and polyadenylation of the pre-mRNA with release of RNA polymerase II. The other options mix up which polymerase is involved or omit the processing step in eukaryotes.