ne102 2/27 + 3/2 lecture 10/11 - transcription: promoters, TFs + RNA processing; from RNA to protein

where is promoter found?

found on the strand that is NOT the template, 35 nucleotides away from start site, helps RNA poly identify which strand has gene of interest → transcribe certain genes

what’s a gene?

sequence of nucleotides on one DNA strand that’s transcribed into an RNA molecule

what does it mean to transcribe a gene?

to “rewrite” the sequence of DNA nucleotides in one gene using RNA language (AU GC); by using the complementary strand as a template, you can synthesize RNA strand w/ gene of interest

what do transcription factors do?

bind to promoter + help RNA poly bind to DNA → prep DNA + RNA poly

how does transcription start in eukaryotic cells?

TATA box recognized + TBP + TFIID binds to it → binds to TFIIB, RNA poly can interact w/ TFs + DNA → DNA bends + can be recognized by RNA poly

other TFs bind to optimize RNA poly attachment/activity

TFIIE → TFIIH → unwinds DNA + modifies RNA poly for activity; TFIIF prevents random binding of RNA poly to non-specific DNA regions

when does transcription start?

energy from hydrolysis of ATP → RNA poly “closes” around the unwinded DNA → RNA poly detaches from all TF to start transcription

elongation factors

allow RNA poly II to move through DNA that’s packaged into nucleosomes

mRNA processing

preparing the synthesized RNA for translation

challenges to mRNA processing

mRNA needs to leave nucleus + include only the coding sequence of the protein → mRNA needs to be modified for translation to start

solutions to challenges

1. mRNA Processing helps mRNA leave nucleus

2. capping + polyadenilation → includes only coding sequence of protein

3. splicing → modifies mRNA for translation to begin

phosphorylation of RNA poly

allows RNA processing proteins to assemble on its tail as RNA is synthesized (negative charge = changes conformation + attracts other proteins)

step 1

5’ capping, RNA modifying molecules are recruited on RNA pol, ready to modify newly made mRNA

RNA 5’ capping

RNA modified to facilitate mRNA transport to cytosol + correct translation

step 2

splicing, removal of introns → RNA is modified

exons

coding regions of the gene, carry genetic info for protein making

what does RNA poly transcribe

entire gene

RNA splicing

removal of introns (noncoding regions) in the middle of RNA sequence, ONLY for eukaryotic cells = RNA modification

lariat structure

during splicing, 2’ OH group creates a loop w/ 5’ splice site → intron spliced, exon joins together → mRNA encodes for protein

spliceosomes

how snRNP can tag beginning + end of introns for removal, made of snRNPs + snRNA

when does RNA splicing occur?

during transcription

polyadenylation

polyadenylation factors act last, adding polyA tail to 3’ UTR

mRNA transport

after splicing, mRNA binds exon junction complex (EJC) to pass nuclear pore complex

transcription recap for eukaryotes

exons/introns → transcription to pre-mRNA → capping, splicing, polyadenylation → export → translation