Modelling Reveals Kinetic Advantages of Co-Transcriptional Splicing
Figure 1
Post-transcriptional and co-transcriptional splicing.
A) Spliceosome assembly begins with the U1 and U2 snRNPs. On the post-transcriptional splicing pathway, polyadenylated pre-mRNA is spliced (step one) to produce polyadenylated lariat-exon2, from which mature mRNA results on completion of step two. B) Splicing can occur during transcript elongation on the co-transcriptional splicing pathway. The RNA polymerase Pol II (shown in green) transcribes Exon1, the Intron and Exon2 (colours of the RNA indicate the corresponding region of the DNA, and the red oval indicates the cap on the 5′ end of the RNA). Splicing can occur after the transcription of specific sequences that trigger the assembly and activation of the spliceosome on the RNA. C) The transcription and splicing pathway. A polymerase proceeds from the active promoter complex (APC) through 15 irreversible steps that represent the transcription of nucleotides in Exon 1 and the Intron up until the branchsite. From the branchsite () until the end of Exon 2, a transition can be made to the co-transcriptional splicing path
as the first step of splicing can occur. The characteristics of post-transcriptional splicing steps one and two (
and
), and co-transcriptional splicing step two (
) are determined by model comparison.