Transcriptional termination in the Balbiani ring 1 gene is closely coupled to 3'-end formation and excision of the 3'-terminal intron.
We have analyzed transcription termination, 3'-end formation, and excision of the 3'-terminal intron in vivo in the Balbiani ring 1 (BR1) gene and its pre-mRNA. We show that full-length RNA transcripts are evenly spaced on the gene from a position 300 bp upstream to a region 500-700 bp downstream of the polyadenylation sequence. Very few full-length transcripts and no short, cleaved, nascent transcripts could be observed downstream of this region. Pre-mRNA with 10-20 adenylate residues accumulates at the active gene and then rapidly leaves from the gene locus. Only polyadenylated pre-mRNAs could be detected in the nucleoplasm. Our results are consistent with the hypothesis that transcription termination occurs in a narrow region for the majority of transcripts, simultaneous with 3'-end formation. Excision of the 3'-terminal intron occurs before 3'-end formation in about 5% of the nascent transcripts. When transcription terminates, 3' cleavage takes place and 10-20 adenylate residues are added, the 3'-terminal intron is excised from additionally about 75% of the pre-mRNA at the gene locus. Our data support a close temporal and spatial coupling of transcription termination and the cleavage and initial polyadenylation of 3'-end formation. Excision of the 3'-terminal intron is highly stimulated as the cleavage/polyadenylation complex assembles and 3'-end formation is initiated.
Baurén
G
G
Department of Molecular Genome Research, Stockholm University, S-106 91 Stockholm, Sweden.
Belikov
S
S
Wieslander
L
L
D000818:Animals; D002683:Chironomidae / Q000235:genetics* / Q000378:metabolism; D017344:Genes, Insect; D019476:Insect Proteins / Q000096:biosynthesis / Q000235:genetics*; D007438:Introns; D016133:Polymerase Chain Reaction; D012322:RNA Precursors / Q000096:biosynthesis / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D012469:Salivary Glands / Q000378:metabolism; D017384:Sequence Deletion; D014158:Transcription, Genetic
C074746:Balbiani Ring 1 protein, Chironomus tentans; D019476:Insect Proteins; D012322:RNA Precursors