Summarizing Prokaryotic Transcription

Summary

In prokaryotes, mRNA synthesis is initiated at a promoter sequence on the DNA template comprising two consensus sequences that recruit RNA polymerase. The prokaryotic polymerase consists of a core enzyme of four protein subunits and a σ protein that assists only with initiation. Elongation synthesizes mRNA in the 5' to 3' direction at a rate of 40 nucleotides per second. Termination liberates the mRNA and occurs either by rho protein interaction or by the formation of an mRNA hairpin.

Glossary

consensus

DNA sequence that is used by many species to perform the same or similar functions

core enzyme

prokaryotic RNA polymerase consisting of α, α, β, and β' but missing σ; this complex performs elongation

downstream

nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3' end relative to a site on the mRNA

hairpin

structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides

holoenzyme

prokaryotic RNA polymerase consisting of α, α, β, β', and σ; this complex is responsible for transcription initiation

initiation site

nucleotide from which mRNA synthesis proceeds in the 5' to 3' direction; denoted with a “+1”

nontemplate strand

strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

plasmid

extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes

promoter

DNA sequence to which RNA polymerase and associated factors bind and initiate transcription

Rho-dependent termination

in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template

Rho-independent

termination sequence-dependent termination of prokaryotic mRNA synthesis; caused by hairpin formation in the mRNA that stalls the polymerase

TATA box

conserved promoter sequence in eukaryotes and prokaryotes that helps to establish the initiation site for transcription

template strand

strand of DNA that specifies the complementary mRNA molecule

transcription bubble

region of locally unwound DNA that allows for transcription of mRNA

upstream

nucleotides preceding the initiation site; in general, sequences toward the 5' end relative to a site on the mRNA