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).