the spliceosome and its splicing cycle Flashcards
what is pre-mRNA splicing catalyzed by?
the spliceosome
what is the spliceosome?
a multi megadalton ribonucleoprotein (RNP) complex comprised of 5 snRNPs and numerous proteins
is the spliceosome complex permanent?
no
why is there no U3?
U3 is a snoRNP. It is thought to guide site-specific cleavage of ribosomal RNA during the pre-rRNA processing unlike other snoRNAs that participate in RNA 2’-O-methylation
what does U7 do?
U7 small RNA is involved in processing the 3’ stem loop of histone pre-mRNA
who was stephanie smith?
Diagnosed with systemic lupus erythematosus (SLE)
She produced antibodies to a set of nuclear proteins instead of to DNA
Thus, the Smith Antigen was born
what is the smith antigen made of?
omplex of RNA and multiple proteins
what are the RNAs in the smith antigen?
U1, U2, U4, U5, U6
what does U1 do?
recognizes the 5’ end (GU).
what does U2 do?
identifies the branch point adenosine
what does U4 do?
prevents U6 from interacting with U2
what does U5 do?
interacts with the 5’ after replacement of U1
what does U6 do?
interacts with U2 to activate
what is the 3’ end of the intron bound to?
non-snRNP proteins; branch point binding protein (BBP) and U2 auxiliary factor (U2AF).
what is complex A/ pre spliceosome?
U2 displaces BBP and a mismatch occurs between U2 and the branch point
what is complex B / pre catalytic?
The U4 U5 U6 displaces the U2AF and U2 starts to pair with U6
what is prp8?
argest and most conserved protein splicing factor and occupies a central position within the tri-snRNP. Organizes the U4 U5 U6. has 4 domains
what is complex B* / active spliceosome?
The pre-mRNA rearranges and U1 is released. The 5’ end of the intron moves to the active site. U4 unwinds from U6 while U2 and U6 associate more tightly to put the adenosine in the active site
what is complex C/ catalytic spliceosome?
The first transesterification occurs and the branched intron forms
what happens after complex C?
, more rearranging and a second transesterification releases the intron in lariat
where does transcription of RNA occur?
nucleus
where does protein synthesis occur?
cytoplasm
what is U6 transcribed by and does it stay in the nucelus or is it tarnsported out?
transcribed by RNAP3 - stay in nucleus
what is U2, U4, U1, U5 transcribed by and does it stay in the nucelus or is it tarnsported out?
transcribed by RNAP2 - sent to cytoplasm where Sm proteins bind and promote the hypermethylation of the 5’ cap
