Lecture 6- RNA splicing Flashcards
when and where are mRNAs modified
before elongation, at the 5’ end
RNA capping
first modification, involves methylation at the phosphate group of a nucleotide, increasing molecule hydrophobicity
why are polyAs useful
protection, as well as allowing PABPs to bring the caps together, helping to initiate translation
lariat splicing
intron cut at 5’, formation of a loop-like lariat structure
cut at 3’- exons can then be joined
introns are debranched
what happens to introns
either degraded, or used as regulatory RNA
what does ‘spliceosome’ refer to
the molecules which aid in splicing, such as snRNPs (ribonucleoproteins) with catalytic functions or splicing factors
example of an snRNP and its function
U1- recognises the 5’ splice site by base pairing
U2- binds closer to the 3’ site, but not directly- causes bulging, then auxiliary U2 factor helps it find the branchpoint
what ultimately leads to the lariat forming
complex of these ribonucleoproteins forms, catalyses trans-esterification reactions to form a lariat
role of proteins in lariat formation
a lot of changing states of snRNPs, e.g. bridging them, arranging RNAs, releasing components
what links U1 and U2
SR proteins with RNA recognising regions
does pre-mRNA linkage occur through exons or introns?
either
example of a way introns can become defined
spliceosome rearrangement due to steric encumbrance- if the arrangement of an exon means normal splicing can’t occur, introns become defined by the spliceosome instead
what is back-splicing and when does it occur
formation of circular RNAs
facilitated by exon-definition complexes, and only happens when there are many, or long, exons- these are not remodelled to intron spanning complexes
uses for circRNAs
as ‘sponges’, e.g. by mimicking sites
attracting miRNAs
recruitment of proteins, as part of enhancers, etc
how can the spliceosome differ from the normal U1/U2 etc system
alternative spliceosome using U11 and 12 instead of 1 and 2
