Choice of 3' cleavage/polyadenylation site in beta-tropomyosin RNA processing is differentiation-dependent in mouse BC3H1 muscle cells.
The rodent beta-tropomyosin (TM) gene produces either a 1.2-kilobase (kb) skeletal muscle beta-TM mRNA or a 1.1-kb fibroblast/smooth muscle TM-1 mRNA through tissue-specific alternative exon splicing and 3' cleavage/polyadenylation at two alternative poly(A) sites. beta-TM mRNA contains exon 6b, 9a, and the poly(A) site immediately following exon 9a, whereas TM-1 mRNA contains exon 6a, 9b, and the poly(A) site following exon 9b. We isolated a novel 2.1-kb beta-TM cDNA clone, pUTM, from a cDNA library of 2-day differentiated mouse BC3H1 muscle-like cells. This cDNA contains the entire sequence of mature beta-TM mRNA with a normal but unused poly(A) site associated with exon 9a. Instead, 3' cleavage/polyadenylation of this cDNA occurred at the exon 9b-associated distal poly(A) site, resulting in the retention of a 1-kb intron and the TM-1 exon 9b. We identified a 2.3-kb functional mRNA, UTM RNA, corresponding to pUTM. UTM RNA appeared early during BC3H1 cell differentiation and gradually decreased as the beta-TM mRNA increased. UTM RNA was also detected in mouse C2C12 muscle cells and in skeletal muscle tissue isolated from mouse leg. Thus, in the processing of beta-TM gene transcripts, selection of alternative terminal exons and alternative poly(A) sites are not necessarily linked as they appear to be in other gene systems.
Wang
Y C
YC
Department of Biochemistry, University of Iowa College of Medicine, Iowa City 52242.
Rubenstein
P A
PA
D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D002454:Cell Differentiation; D004247:DNA / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D011061:Poly A / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012326:RNA Splicing; D015183:Restriction Mapping; D014158:Transcription, Genetic; D014335:Tropomyosin / Q000235:genetics* / Q000378:metabolism
D014335:Tropomyosin; D011061:Poly A; D004247:DNA