Chapter 13Transcription

RNA in the Primeval WorldWhat came first proteins or nucleic acids?

or

chicken

Or the………

EGG!

Life’s Paradox…

1981: Tomas Cech Discovered:n RNA could act as enzymes=Ribozymes!

Ribozyme

RNA

Tetrahymena thermophila

RNA structureReminder of RNA structure.

What are differences between DNA and RNA?

Review Question:

RNAs

Functional Informational

transfer RNAsVital for protein translation

ribosomal RNAsForms complexes with proteins

Vital for protein translation

messenger RNAsIntermediates in decoding genes into proteins

And now

many more!

TRADITIONAL CLASSIFICATION of RNAs

Additional functional classes of RNA

n Small nuclear RNAs

n Small nucleolar RNAs

n Small cytoplasmic RNAs

n Small Interfering RNAs

n MicroRNA

n snRNAs

n snoRNA

n scRNA

n siRNA

n miRNA

Molecule of the year2002

RNA Transcription

Transcription is always 5’ to 3’!

The Basic Model

Let’s look closely at the process of transcription.

terminator

Transcription unit with more detail

Four key components of transcription

n Promoter

n Transcription start site

n RNA coding region

n The Terminator

Process of Bacterial Transcription

n Initiation

n Elongation

n Termination

Prokaryotic Initiation

Prokaryotic: RNA Polymerase

Required for Initiation of Transcription

Can only continue transcription

ω ω

RNA polymerase binds

Prokaryotic Elongation

The Search

The Binding: “Closed Complex”

The Unwinding:“Open complex”

Transcription Begins: Sigma factor leaves

RNA Polymerase

ω

Transcription is always 5’ to 3’

Prokaryotic Termination

Transcription Termination

n 2 mechanismsq rho dependentq rho independent

Rho Dependent

Binding of rho protein

Secondary RNA structure

Rho protein has helicase activiity!

Rho Independent

Speed bump

Eukaryotic Transcription

Eukaryotic Initiation

Promoter of RNA polymerase II

Affects rate of transcription

Promoter recognition and transcription initiation

■BASAL TRANSCRIPTION APPARATUS

□General Transcription Factors

□RNA Polymerase

□Mediator proteins

■Transcriptional Activator Proteins

General Transcription Factors(for example: for RNA Polymerase II)

1. TFIIA

2. TFIIB

3. TFIID

4. TFIIE

5. TFIIF

6. TFIIH

Binds to minor groove

Eukaryotic Transcriptional Termination

n Protein dependent terminationq But proteins binds DNA not RNA

n Protein Independentq but no hairpin loop

n Eukaryotesn Arachae

n Eubacteria

Evolution and Regulatory Sequences

TATA BINDING PROTEINS

NO TATA BINDING PROTEINS