Transcription DNA

8/13/2019 Transcription DNA

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Lecture materials may be downloaded from:

http://www.msi.upd.edu.ph/claroline/

Username: MS272

Password: student

The transcription of genes


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DNA

The central dogma of molecular biology

transcription translation

replication

reverse-transcription

replication

RNA protein

DNA

Types of RNA

transcription

translation

mRNA protein

tRNA

rRNA

other types


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The transcription of genes:prokaryotes

Key proteins involved in thetranscription of bacterial genes

RNA polymerase, core enzyme

two subunits, one subunit,

one subunit, [one subunit]

sigma factor,

RNA polymerase + sigma factor holoenzyme

synthesizes all 3 classes of RNA

(mRNA, tRNA, rRNA)


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Structure ofeubacterial

RNA polymerases

Transcription unit

A sequence of DNA transcribed into a single RNA, startingat the promoter and ending at the terminator


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Promoter - region of DNA involved in binding

of RNA polymerase to initiate

transription

Functions of a promoter

The promoter determines:

Which strand will serve as a template.

Transcription starting point.

Strength of polymerase binding.

Frequency of polymerase binding.


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Four stages of transcription

1

2

3

4

template recognition

initiation

elongation

termination

Template recognition

forming the closedpromoter complex


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Template recognition

RNA polymerase recognizes promoters

based on consensus sequences

consensus sequence an idealizedsequence in which each positionrepresents the base most often foundwhen many actual sequences are

compared

- 10 box- 35 box


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Transcription bubble


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Contact points between the sigma factorand a typical prokaryotic promoter

HOOC NH2


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Initiation of transcription

formation of open complex

initial synthesis

loss of sigma factor

promoter clearance

RNA polymerase moves like an inchwormduring elongation

Back end moves 1bp per nucleotideadded to RNA

Front end movesseveral bpdiscontinuously


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RNA synthesis

Termination of transcription

How does the RNA polymeraseknow when to stop?

Types (based on in vitro experiments):

intrinsic terminators - no proteins (factors) required

rho-dependent - rho factor required

TERMINATORS - sequences at which

transcription stops and thecomplex dissociates


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Intrinsic terminators: structural features

hairpin-forming (palindromic, inverse-repeat)region

a run of U residues

Intrinsic terminators: structural features


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Principal feature: C-rich, G-poor sequence

preceding actual termination site

rho-dependent terminators

Hot-pursuit modelfor rho-dependent

termination


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Coupling of transcription and translationin prokaryotes

The transcription of genes:

eukaryotes


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Transcription

Pre-mRNA processing

Transport to the cytoplasm

The generation of mature mRNAsinvolves the following major steps

1. transcription

the eukaryotic RNA polymerases

the transcription factors

promoters and enhancers

stages

chromatin remodeling

initiation of transcription

elongation termination

2. pre-mRNA processing

capping

splicing

polyadenylation

3. transport to the cytoplasm


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Type of Polymerase Product Location

RNA Polymerase I pre-rRNA (except 5S) nucleolus

RNA Polymerase II pre-mRNA (hnRNA) nucleoplasm

RNA Polymerase III tRNA, 5S rRNA, etc. nucleoplasm

Types of eukaryotic RNA polymerases


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Transcription factor - any protein other than RNA Polymerase

that is required for transcription

may bind to RNA Polymerase

may bind to another transcription factor

may bind to cis-acting DNA sequences may bind to effectors

RNA pol II cannot initiate transcription by itself;

requires auxilliary transcription factors to

initiate transcription.

General factors - required for initiating transcription at all

promoters

Upstream factors - ubiquitous factors that increase the

efficiency of transcription initiation; set of

factors unique to each promoter

Inducible factors - act in the same manner as an upstream

factor but their synthesis is regulated in a

temporal or spatial manner

Transcription factorsTypes of transcription factors:(according to their importance to transcription initiation)

Basal transcription apparatus - RNA polymerase + general

factors both needed to initiate

transcription


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Major types of DNA-binding domains

(motifs found in the sequences)

zinc finger

helix-turn-helix

amphipathic helix-loop-helix

leucine zippers


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helix-turn-helix

zinc finger

leucine zipper

Promoters vs. enhancers


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Initiation of transcription

ordered sequence of assembly of

initiation complex

phosphorylation of the C-terminal

domain (CTD) tail of RNA polymerase II

(may be needed for promoter clearance)

Assembly ofinitiationcomplex


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Elongation of transcript

phosphorylation ofthe CTD tail ofRNA polymerase II

CPSF

CPSF = cleavage and polyadenylation specificity factor

Termination and polyadenylation


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Pre-mRNA processing: capping

Caps may differ in number of methylations

Pre-mRNA

processing:

splicing

Spliceosomes

consist of

snRNPs


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Conserved signals at intron-exon junctions

Translation of mRNA in the cytoplasm


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Next meeting

Translation of mRNAs

Transcription DNA

Documents

Transcript of Transcription DNA