title: Isolation of rat testis cDNAs encoding an insulin-like growth factor I precursor.
abstract: We have characterized rat testis cDNAs encoding insulin-like growth factor I (IGF-I) precursor to facilitate studies of IGF-I expression in the male reproductive system. Two clones, P2 and P3, with inserts of 786 and 1200 bp, respectively, were isolated from a lambda gt11 library of rat testis cDNAs. The longest open reading frame of cDNA P2 predicts a 153-amino-acid residue IGF-I precursor that has only 11 amino acid substitutions compared with a human IGF-IA precursor encoded by a human liver mRNA. Three substitutions are within the predicted rat IGF-I sequence: a Pro for Asp in the B domain, an Ile for Ser in the C domain, and Thr for Ala in the D domain. Only two substitutions distinguish the predicted rat sequence from a mouse liver IGF-IA precursor: Thr for Ala in the signal peptide and Ala for Ser in the D domain. P2 hybridizes with poly(A)+ mRNAs of 7.5, 4.7, 1.7, and 1.2-0.9 kb in rat liver and testis. The other testis cDNA, P3, appears to represent a partially processed rat IGF-I mRNA precursor. By comparing the sequence of cDNA P2 with that of cDNA P3 and a 2.3-kb rat IGF-I genomic fragment, we predict exon splice sites within the codon for residue 26 and between residues 86-87 of the rat IGF-I precursor. Both of the predicted splice sites align with exon-intron junctions in the human IGF-I gene. We conclude, therefore, that IGF-I is synthesized as a precursor in the rat testis and that the structure of IGF-I genes, mRNAs, and precursors are highly conserved across species.
mesh_terms: D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D005796:Genes; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000235:genetics; D012326:RNA Splicing; D051381:Rats; D012689:Sequence Homology, Nucleic Acid; D013002:Somatomedins / Q000235:genetics*; D013737:Testis / Q000502:physiology*
chemical_list: D011498:Protein Precursors; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D004247:DNA