Chapter 8: RNA Synthesis & Processing

RNA Synthesis & Processing begins by outlining the fundamental mechanisms of transcription in prokaryotes, using E. coli as a model to explain how RNA polymerase and the sigma subunit recognize specific promoter sequences to initiate RNA chains de novo. The text contrasts this with the complexity of eukaryotic transcription, which employs three distinct nuclear RNA polymerases—Pol I, II, and III—to transcribe specific classes of genes, including ribosomal, messenger, transfer, and noncoding RNAs. A significant portion of the summary is dedicated to the intricate assembly of the preinitiation complex for RNA polymerase II, detailing the recruitment of general transcription factors like TFIID, TBP, and TFIIH, and the essential phosphorylation of the C-terminal domain (CTD) to trigger elongation. The discussion extends to the critical post-transcriptional modifications required for eukaryotic RNA maturity, including the nucleolar processing of rRNAs and tRNAs involving snoRNPs and the catalytic ribozyme RNase P. The chapter thoroughly explores coupled mRNA processing events such as the addition of the 7-methylguanosine 5-prime cap and 3-prime polyadenylation. Furthermore, it elucidates the mechanism of pre-mRNA splicing, describing how the spliceosome—composed of snRNPs and snRNAs—excises introns via lariat intermediates. The summary also highlights the diversity generated through alternative splicing, the evolutionary significance of self-splicing introns, and the regulation of gene expression through RNA editing and cytoplasmic mRNA degradation stability control.