RIBOFLAVINURIA IN THE RD CHICKEN - 5'-SPLICE SITE MUTATION IN THE GENE FOR RIBOFLAVIN-BINDING PROTEIN

Eggs of oviparous species must contain all components required for nor mal embryonic development. Among these, the vitamin riboflavin is depo sited into egg white and yolk bound to the carrier protein, riboflavin -binding protein (ribBP). We have begun to investigate the mechanisms underlying ribBP transport pathways by molecular characterization of a relevant mutation in chicken. The autosomal recessive rd allele in Ga llus gallus domesticus prevents the synthesis of functional ribBP and induces embryonic death on day 13. Polymerase chain reaction primers d erived from the previously determined wild type cDNA sequence were use d to amplify and clone cDNAs for ribBP from normal (Rd) and deficient (rd) animals. The rd allele was associated with a 100-nucleotide delet ion in the messenger RNA for ribBP. Genomic clones were generated via polymerase chain reaction using primers flanking this 100-base pair de letion, and the resulting 2.1-kilobase pair clones were sequenced. The deletion in the rd ribBP cDNA corresponds precisely to an exon. The s plice site following this exon contains a G --> A mutation at position 1 of the downstream 5'-splice donor sequence. The effect of this anom aly and the cause of the rd phenotype is the loss of the 100-base pair exon during the splicing process.