Messenger RNA splicing is an essential and complex process for the removal of 
intron sequences. Whereas the composition of the splicing machinery is mostly 
known, the kinetics of splicing, the catalytic activity of splicing factors and 
the interdependency of transcription, splicing and mRNA 3' end formation are 
less well understood. We propose a stochastic model of splicing kinetics that 
explains data obtained from high-resolution kinetic analyses of transcription, 
splicing and 3' end formation during induction of an intron-containing reporter 
gene in budding yeast. Modelling reveals co-transcriptional splicing to be the 
most probable and most efficient splicing pathway for the reporter transcripts, 
due in part to a positive feedback mechanism for co-transcriptional second step 
splicing. Model comparison is used to assess the alternative representations of 
reactions. Modelling also indicates the functional coupling of transcription and 
splicing, because both the rate of initiation of transcription and the 
probability that step one of splicing occurs co-transcriptionally are reduced, 
when the second step of splicing is abolished in a mutant reporter.