Chapter 29: RNA Synthesis & Processing

RNA Synthesis & Processing from Biochemistry (Eighth Edition) provides an in-depth biochemical analysis of RNA synthesis and processing, comprehensively exploring the mechanisms of transcription in both prokaryotes and eukaryotes. The text establishes RNA polymerase as the central enzyme catalyzing the formation of phosphodiester bonds to synthesize RNA transcripts from DNA templates, a process occurring in three stages: initiation, elongation, and termination. In prokaryotic systems like E. coli, the discussion details how the sigma subunit guides the polymerase holoenzyme to specific promoter sequences, such as the minus 10 and minus 35 regions, and how transcription is terminated via hairpin loops or the rho protein. The pharmacological relevance of transcription is highlighted through the mechanisms of antibiotics like rifampicin and actinomycin D, which inhibit bacterial gene expression. Moving to eukaryotic transcription, the chapter differentiates the specialized roles of RNA polymerases I, II, and III in synthesizing ribosomal, messenger, and transfer RNAs, respectively, and explains the assembly of complex initiation machinery involving the TATA-box-binding protein and various transcription factors. A significant portion of the chapter is dedicated to the extensive post-transcriptional processing required for eukaryotic mRNA, including the addition of a 5-prime cap and a 3-prime poly(A) tail to enhance stability and translation. The intricate mechanism of splicing is broken down, describing how spliceosomes composed of small nuclear ribonucleoproteins (snRNPs) remove non-coding introns and join exons via transesterification reactions involving lariat intermediates. The text further explores how alternative splicing generates proteomic diversity from a single gene, as seen in calcitonin production, and examines the clinical implications of splicing mutations in diseases such as thalassemia. Finally, the chapter addresses RNA editing, where nucleotide sequences are altered after transcription, and concludes with the evolutionary discovery of catalytic RNA, or ribozymes, which demonstrate that RNA can function as an enzyme capable of self-splicing.