Lect 2 Bacterial Transcription

8/10/2019 Lect 2 Bacterial Transcription

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Transcription

DNA-directed synthesis of RNA

All human RNAs are transcribed from DNA

templates

TYPE of RNA FUNCTION

Ribosomal RNA (rRNA) Components of ribosome

Transfer RNA (tRNA) Delivery of amino acidsMessenger RNA (mRNA) Template for protein synthesis

Short nuclear RNAs (snRNAs) Components of spliceosome

Short interfering RNAs (siRNAs) or

micro RNAs (miRNAs)

Regulation of gene expression

Short nucleolar RNAs (snoRNAs) Methylation of rRNAs

Not necessarily true for viruses (ex. HIV, HepB) --> some viruses have RNA genes/used as templates


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S#6a&6I#6( J(&E "6 TKH*&(("6L )%& ?&_74@Sequence of RNA transcript is parallel to non-template

strand


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S#6a&6I#6( J(&E "6 TKH*&(("6L )%& ?&_ parallel to AUG in RNA transcript


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Bacterial RNA Polymerase (RNAP)

Synthesizes all RNA except primers for replication

Positively-charged

cleft binds DNA

Mg2+in active site

!"

Thermus thermophilusRNAP

Core enzyme: !2""'#

(alpha2, sigma, sigma, omega)

DNA non-template

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)&'H24)&

RNA

------------- -------------

beta beta'

4 diff proteins to form 1

polymerase


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RNAP core enzyme

!factor recognizes promoters

RNAP holoenzyme

$is extended and interacts with -35 and -10

regions Rainbow coloured coils stretching across entire DNA section along enzyme


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?


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DJ Koslover et al.(2012) J Mol Biol423:664-76

Model of Rho-mediated termination

Rho recognizes rut site, then

closes around RNA and

advances toward RNAP

Rho causes allosteric changein RNAP that releases

template


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Operons

Operon (in bacteria): two or more genestranscribed together as one RNA molecule

The mRNA is polycistronic

Genes in an operon usually have related

functions


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Overview of bacterial transcription

$dissociates

Fig 12-3 from Watson et al., Molecular

Biology of the Gene, 6thed.


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Summary of bacterial transcription

Transcription of genes is carried out by RNApolymerase (RNAP), a multisubunit complex

Bacterial RNAP recognizes promoters with a

defined consensus sequence via the $subunit

DNA strands are separated and RNA synthesis

occurs, possibly after abortive initiation

Termination is mediated by a termination hairpin

structure or by Rho factor

Lect 2 Bacterial Transcription

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