As. Lewin et al., COTRANSCRIPTIONAL SPLICING OF A GROUP-I INTRON IS FACILITATED BY THE CBP2 PROTEIN, Molecular and cellular biology, 15(12), 1995, pp. 6971-6978
The nuclear CBP2 gene encodes a protein essential for the splicing of
a mitochondrial group I intron in Saccharomyces cerevisiae. This intro
n (bI5) is spliced autocatalytically in the presence of high concentra
tions of magnesium and monovalent salt but requires the Cbp2 protein f
or splicing under physiological conditions. Addition of Cbp2 during RN
A synthesis permitted cotranscriptional splicing. Splicing did not occ
ur in the transcription buffer in the absence of synthesis. The Cbp2 p
rotein appeared to modify the folding of the intron during RNA synthes
is: pause sites for RNA polymerase were altered in the presence of the
protein, and some mutant transcripts that did not splice after transc
ription did so during transcription in the presence of Cbp2. Cotranscr
iptional splicing also reduced hydrolysis at the 3' splice junction. T
hese results suggest that Cbp2 modulates the sequential folding of the
ribozyme during its synthesis. In addition, splicing during transcrip
tion led to an increase in RNA synthesis with both T7 RNA polymerase a
nd mitochondrial RNA polymerase, implying a functional coupling betwee
n transcription and splicing.