Dynamic organization of pre-mRNA splicing factors.

Studies from several laboratories during the past few years have increased our understanding towards the dynamic organization of pre-mRNA splicing factors in the mammalian cell nucleus. Many well characterized splicing factors have been localized in a speckled pattern in the cell nucleus. Upon the activation of RNA polymerase II transcription, splicing factors are recruited to the sites of transcription from sites of reassembly and/or storage. Nascent intron-containing RNA transcripts are spliced at the sites of transcription. The speckled distribution of splicing factors in the nucleus is altered when either transcription or pre-mRNA splicing activities are interrupted suggesting that the organization of the splicing machinery in the interphase nucleus is a direct reflection of the transcriptional activity of the cell.