Multiple polyadenylation sites in a Drosophila tropomyosin gene are used to generate functional mRNAs.
The gene encoding muscle tropomyosin I in Drosophila is alternatively spliced in embryonic and thoracic muscle to generate two sizes classes of RNAs. By Northern blot analysis, the embryonic RNA class shows a broad RNA band of hybridization of 1.3 kb and a more sharply defined, less abundant RNA band at 1.6 kb. The thoracic class of RNAs, on the other hand, consists of a broad hybridization band at 1.7 kb and a more sharply defined band at 1.9 kb. Each size class of RNA encodes a different tropomyosin isoform. The two classes of alternatively spliced RNAs utilize the same 3' terminal exon of the gene. The DNA sequence of this exon reveals a cluster of several polyadenylation signals (AAUAAA) or polyadenylation-like signals. We show here by S1 nuclease protection analysis that at least five and possibly seven of these polyadenylation or polyadenylation-like sequences are associated with in vivo embryonic and thoracic mRNA cleavage processing sites. Six of these S1 sites are clustered within 119 bp and a seventh is located 255 bp downstream. At least one of the polyadenylation-like signal sequences appears to be an unusual AACAAA sequence. In addition we also show that these mRNAs function in vitro to synthesize muscle tropomyosins.
D000818:Animals; D001483:Base Sequence; D004330:Drosophila; D005470:Fluorometry; D009693:Nucleic Acid Hybridization; D011061:Poly A / Q000032:analysis*; D014176:Protein Biosynthesis; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism*; D014335:Tropomyosin / Q000235:genetics*
D012333:RNA, Messenger; D014335:Tropomyosin; D011061:Poly A