Splicing of Balbiani ring 1 gene pre-mRNA occurs simultaneously with transcription.
The 40 kb Balbiani ring 1 (BR1) gene is at a given moment transcribed by, on average, 120 RNA polymerases. Here we directly assay the excision of introns both in the nascent and in the released nucleoplasmic BR1 pre-mRNAs, isolated by microdissection. We show that intron 3, located 3 kb from the 5' end of the pre-mRNA, is excised simultaneous with transcription. Within 2.5 min of transcription time, 50% of the pre-mRNA molecules have lost the intron. Intron 4, located 600 bases from the polyadenylation site, is excised cotranscriptionally in 5%-10% of the molecules and after or during release to the nucleoplasm in the remaining molecules. Our results demonstrate that spliceosome assembly is a cotranscriptional process in vivo and that splicing may occur during transcription but also after completed transcription, depending on the position of the intron.
Baurén
G
G
Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, Sweden.
Wieslander
L
L
D000818:Animals; D001483:Base Sequence; D002683:Chironomidae / Q000235:genetics / Q000378:metabolism; D002874:Chromosome Mapping; D002875:Chromosomes / Q000648:ultrastructure; D004247:DNA / Q000032:analysis / Q000378:metabolism; D017931:DNA Primers; D005091:Exons; D007438:Introns; D007700:Kinetics; D016133:Polymerase Chain Reaction; D012322:RNA Precursors / Q000378:metabolism*; D012326:RNA Splicing; D012333:RNA, Messenger / Q000096:biosynthesis*; D012469:Salivary Glands / Q000378:metabolism / Q000648:ultrastructure; D014158:Transcription, Genetic
D017931:DNA Primers; D012322:RNA Precursors; D012333:RNA, Messenger; D004247:DNA