Practice question

RNA polymerase II is the central eukaryotic polymerase responsible for synthesizing messenger RNA precursors, long noncoding RNAs, many small nuclear RNAs such as U1, U2, U4, U5, and microRNA primary transcripts. Its unique largest subunit RPB1 harbors C-terminal domain of heptapeptide repeats YSPTSPS that undergoes dynamic phosphorylation regulating transcription cycle. Serine5 phosphorylation by TFIIH marks initiation and capping, serine2 phosphorylation by P-TEFb marks elongation and 3' processing. Polymerase II is extremely sensitive to amatoxin alpha-amanitin at 0.01 microgram per milliliter, causing liver failure due to transcriptional arrest.