Chapter 14 RNA Processing I : Splicing

Summary of splicing Transcription Primary transcript  splicing mature transcript Evidences for introns R-loop in the electron microsopic view of chromatin sequencing ; compare genomic DNA and cDNA

Splicing signals and mechanism Lariat structure Introns almost all start with GU and end with AG Branch point Spliceosome ; pre-mRNA, snRNPs (snurps); protein RNA ; U1,2,4,5,6

Spliceosomal pre-mRNA U2 U5 U6

The spliceosome cycle Model for participation of CTD in exon definition - The CTD acts as a platform for the gathering of pre mRNA and splicing factors.

Alternative splicing Ex) Mu RNA; secreted form and membrane-bound form Sex determination in Drosophila ; 8 chromosomes (X/Y, 2, 3, 4 autosomes) male = XY female= XX Sxl activates tra activates dsx to determine female.

Self-splicing RNAs Group I intron Group II intron serendipity Self-splicing RNAs Group I intron Group II intron Thomas Cech ; Nobel prize 1989 Any possibility of contamination of spliceosome in the in vitro transcription?  chemically synthesize the precursor  splicing still occurs Tetrahymena (ciliate)

Group I intron GTP

Spliceosomal pre-mRNA Group II intron U2 U5 U6 Group II intron’s splicing - - - mechanism is similar to pre mRNA’s splicing - They have A at the branch point.

Phe 5’ Is self-splicing RNA true enzyme? Catalytic RNA = Ribozyme M1 RNA of RNase PI Telomerase CoTc 5’ RNaseP