文档介绍：Section G RNA synthesis and processing Transcription in prokaryotes Transcription in eukaryotes: an overview Transcription in eukaryotes Processing of eukaryotic pre-mRNA Ribosomal RNA Transfer RNA RNA Transcription in Prokaryotes 1. DNA and RNA syntheses are similar in some aspects but different in others Similar in fundamental chemical mechanism: both are guided by a template; both have the same polarity in strand extension (5` to 3`); both use triphosphate nucleotides (dNTP or NTP). Different aspects: No primers are needed; only involves a short segment of a large DNA molecule; uses only one of the plementary DNA strands as the template strand; no proofreading; subject to great variation. 2. The multimeric RNA polymerase in has multiple functions The holoenzyme consists of five types of subunits (a2bb’ s)and its is used to synthesize all the RNA molecules in E. coli. The multiple functions include: searches for initiation sites on the DNA molecule and unwinds a short stretch of DNA (initiation); selects the correct NTP and catalyzes the formation of phosphodiester bonds (elongation); detects termination signals for RNA synthesis (termination). The E. coli RNA polymerase holoenzyme consists of six subunits: a2bb’ s. Possible catalytic subunits Promoter specificity promoter recognition, activator binding kDa 151 155 11 kDa (32-90 kDa) 3. RNA synthesis occurs in a “moving” transcription bubble on the DNA template 4. RNA polymerase recognizes specific promoter sequences on DNA to initiate transcription Promoter sequences are located adjacent to genes. Promoters have two consensus sequences centered at –10 and –35 positions (the first residue of the RNA is given +1).