A CDNA-ENCODING FISH FIBROBLAST GROWTH FACTOR-II, WHICH LACKS ALTERNATIVE TRANSLATION INITIATION

Here, we describe the isolation of a rainbow trout cDNA clone that con tains the entire fibroblast growth factor-2 (FGF-2; basic FGF) coding region. Interestingly, the rainbow trout cDNA contains a translation s top codon just upstream of the primary initiating methionine codon and so cannot give rise to the longer forms of FGF-2 that are produced in mammals by alternative translation initiation at leucines farther ups tream, Transfection of human FGF-2 cDNA into fish cells shows that fis h cells can initiate protein synthesis at an upstream leucine CUG codo n; surprisingly, however, synthesis is initiated only at the most 5' C UG and not at the two subsequent CUG codons or the methionine AUG codo n also used in mammalian cells. Like other FGF-2 proteins, bacterially produced rainbow trout FGF-2 protein binds tightly to heparin-Sepharo se and also promotes the proliferation of fibroblast cells. However, t he protein differs from all others previously identified at amino acid s 121-123, which are part of the proposed highly conserved receptor-bi nding domain. Comparisons of the efficacies of recombinant wild-type a nd mutant rainbow trout FGF-2 proteins demonstrate that these three am ino acids are critical to the activity of FGF-2.