CHMI-2227EL Lecture Notes - Lecture 21: Hydrogen Bond, Tryptophan, Poly(A)-Binding Protein
27 Jun 2018
School
Course
Professor
Biochemistry - Day 21 2018.04.06.
Transcription in Eukaryotes
-The same processes carried out by only one RNA polymerase in E. coli are carried
out in eukaryotes by several similar enzymes
-In addition the activity of eukaryotic transcription complex requires many more
accessory proteins
Eukaryotic RNA polymerases
-Three classes of RNA polymerase are found in
Eukaryotic cells
-All these 3 enzymes are found in the nucleus
-Each type of RNA polymerase synthesizes a different
class of RNA
-RNA polymerase I synthesizes the large ribosomal RNA
(28S, 18S, 5.8 S)
-RNA polymerase II synthesizes messenger RNA
(mRNA) and most small nuclear RNA (snRNA)
-RNA polymerase III synthesizes low molecular weight RNA including the various
transfer RNA and 5S ribosomal RNA
-All 3 types of RNA polymerase are large, complex multimeric proteins (500-700 kDA
*Don’t need to memorize this) consisting of 8-14 different subunits each
-5 subunits are common to all 4 different enzymes
-All 3 types of RNA polymerase recognize different promotors and transcribe distinct
classes of genes
-All 3 types of RNA polymerase posses 2 large subunits, 140 kDa each or greater
-All 3 types of RNA polymerase have sequence similarity to the large beta and beta’
subunits of E.coli RNA polymerase
-The 3 classes of RNA polymerase can be distinguished by their sensitivity to alpha-
amanitin (isolated from a poisonous mushroom)
-A person poisoned by ingestion of these mushrooms
shows no immediate symptoms, but liver function
deteriorates over the following days dye to the lack of
production of new mRNA’s necessary to direct
continuing protein synthesis (liver transplant operation)
-alpha-amanitin blocks RNA chain elongation
-Eukaryotic RNA polymerases cannot initiate
transcription by themselves
-They require the assistance of protein transcription factors (tf’s) to start the synthesis
of and RNA chain
-These transcription factors must bind to a promoter region in DNA and form an
appropriate initiation complex before RNA polymerase will bind and initiate
transcription
-Different promoters and transcription factors are utilized by RNA polymerases
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The same processes carried out by only one rna polymerase in e. coli are carried out in eukaryotes by several similar enzymes. In addition the activity of eukaryotic transcription complex requires many more accessory proteins. Three classes of rna polymerase are found in. All these 3 enzymes are found in the nucleus. Each type of rna polymerase synthesizes a different class of rna. Rna polymerase i synthesizes the large ribosomal rna (28s, 18s, 5. 8 s) Rna polymerase ii synthesizes messenger rna (mrna) and most small nuclear rna (snrna) Rna polymerase iii synthesizes low molecular weight rna including the various transfer rna and 5s ribosomal rna. All 3 types of rna polymerase are large, complex multimeric proteins (500-700 kda. *don"t need to memorize this) consisting of 8-14 different subunits each. 5 subunits are common to all 4 different enzymes. All 3 types of rna polymerase recognize different promotors and transcribe distinct classes of genes.
