Transcription and pre-mRNA splicing are extremely complex multimolecular 
processes that involve protein-DNA, protein-RNA, and protein-protein 
interactions. Splicing occurs in the close vicinity of genes and is frequently 
cotranscriptional. This is consistent with evidence that both processes are 
coordinated and, in some cases, functionally coupled. This review focuses on the 
roles of cis- and trans-acting factors that regulate transcription, on 
constitutive and alternative splicing. We also discuss possible functions in 
splicing of the C-terminal domain (CTD) of the RNA polymerase II (pol II) 
largest subunit, whose participation in other key pre-mRNA processing reactions 
(capping and cleavage/polyadenylation) is well documented. Recent evidence 
indicates that transcriptional elongation and splicing can be influenced 
reciprocally: Elongation rates control alternative splicing and splicing factors 
can, in turn, modulate pol II elongation. The presence of transcription factors 
in the spliceosome and the existence of proteins, such as the coactivator PGC-1, 
with dual activities in splicing and transcription can explain the links between 
both processes and add a new level of complexity to the regulation of gene 
expression in eukaryotes.