Post-Elongation Processing of the Transcript
Species Homo sapiens
Post-transcriptional splicing of introns is affected neither by the elongating properties of RNA polymerase II, nor by the binding of splicing regulatory factors to the enzyme. It is only affected by the relative abundance of constitutive and/or regulatory splicing factors at the sites where splicing takes place. Nevertheless it is important to point out that cytological evidence indicates that unspliced or partially spliced pre-mRNAs do not diffuse in the nucleoplasm far from the transcription sites. Therefore, recruitment of splicing factors to transcription sites would still favor the post-transcriptional splicing of introns.