lec 7.1 - transcription in eukaryotes

transcription in eukaryotes - general features

• happens in nucleus unlike prokaryotes which don’t have nucleus

• must open chromatin structure (push histones/nucleosomes away)

• RNA polymerase in eukaryotes can NOT read DNA to find promoter sequence (unlike prokaryotes) - need transcription factors

• 3 different RNA polymerase - bacteria only employs one

nucleolus

area of genome that has rRNA genes

RNA pol I responsibilities

• responsible for transcribing large rRNA precursors, 16S and 28S

  • situated wherever rRNA genes are transcribed (nucleolus)

  • happens in nucleolus - most active site for rRNA synthesis

RNA pol II responsibilities

• responsible for transcribing most of all protein encoding genes

  • makes heterogenous nuclear RNA (hnRNA) aka pre-mRNA, which gets processed and becomes mature mRNA

  • happens in nucleoplasm/nucleus

RNA pol III responsibilities

• responsible for transcribing genes for tRNAs,

  snRNAs, 5S rRNA and other smaller functional RNAs

  • happens in nucleoplasm/nucleus

Eukaryotic RNA polymerase has

• many basal factors – these bind to DNA – usually only needed for initiation

eukaryotic promoter composition

• has core region that binds RNA polymerase which binds at start point

• enhancer sequences - either upstream or downstream of start site

  • bind activators that activate RNA pol to usually stimulate transcription

• silencer sequences - either upstream or downstream of start site

  • usually repress transcription

RNA pol subunits in bacteria and eukaryotes

• some subunits are common to all classes of eukaryotic RNA polymerases and some are related to bacterial RNA polymerase

in terms of eukaryotic transcription, what component is homologous to sigma in prokaryotes?

• transcription factors

• they bind to specific genes to decide what gets transcribed