EVIDENCE THAT XENOPUS-LAEVIS CONTAINS 2 DIFFERENT NONALLELIC INSULIN-LIKE GROWTH FACTOR-I GENES

Using the polymerase chain reaction (PCR), we have amplified and characterized partial nucleotide sequences of two distinct insulin-like growth factor-I genes (designated IGF-I′ and IGF-I″) from the amphibian, Xenopus laevis. The amplified fragments encoded much of the coding region of the mature peptide (exon III in mammalian IGF-I genes), and exhibited 93% similarity to each other, and 68-82% similarity to mammalian IGF-I amino acid sequences. Southern blot analysis using genomic DNA from a homozygous frog revealed that these two genes are nonallelic in a single organism, like the two nonallelic genes encoding Xenopus insulins that we have characterized previously. Furthermore, both IGF-I mRNAs are expressed in similar quantities in adult liver. © 1990.