title: Structural characterization of exon 6 of the rat IGF-I gene.
abstract: In rat liver, insulin-like growth factor I (IGF-I) mRNAs exist as two major size classes of 7.5-7.0 kb and 1.2-0.9 kb. The 7.5- to 7.0-kb IGF-I mRNAs predominate in some nonhepatic tissues of the rat. Because the previously reported sequences of rat IGF-I cDNAs and genomic clones account for only 2.1 kb of sequence, the majority of the sequence of 7.5- to 7.0-kb rat IGF-I mRNAs was unknown. Using a combination of nucleotide sequencing of genomic DNA and cDNA clones and Northern hybridization and RNase protection, we have characterized a 6,354-base-long 3' exon (exon 6) of the rat IGF-I gene. The sequence of exon 6 establishes the previously unknown sequence of the 3' end of the 7.5- to 7.0-kb rat IGF-I mRNAs, comprised predominantly of an unusually long 3' untranslated sequence (3'UT). The long 3'UT contains multiple ATTTA, A(T)nA, and (T)nA sequences, as well as inverted repeats. These sequences may contribute to the shorter half-life of the 7.5- to 7.0-kb rat IGF-I mRNAs relative to the 1.2- to 0.9-kb forms that have been demonstrated previously in vitro and in vivo. We also demonstrate that the 7.5- to 7.0-kb rat IGF-I mRNAs are localized to the cytoplasm of rat liver, providing indirect evidence that they are mature and functional mRNAs.
authors.affiliation: Department of Pediatrics, University of North Carolina, Chapel Hill 27599.
authors.forename: E C
authors.initials: EC
authors.lastname: Hoyt
authors.forename: J E
authors.initials: JE
authors.lastname: Hepler
authors.forename: J J
authors.initials: JJ
authors.lastname: Van Wyk
authors.forename: P K
authors.initials: PK
authors.lastname: Lund
mesh_terms: D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism; D005091:Exons; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D007438:Introns; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D011061:Poly A / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D012260:Ribonucleases / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
chemical_list: D012333:RNA, Messenger; D011061:Poly A; D007334:Insulin-Like Growth Factor I; D004247:DNA; D012260:Ribonucleases