Coding sequence, genomic organization and expression of a folate binding protein gene in the rat.

The complementary DNA (cDNA) and the gene encoding the folate binding protein alpha isoform (FBPalpha) have been reported for the human and mouse protein. However, there is no information about this gene in the rat, an animal that could be a model to study expression of this protein in vivo when folate metabolism is modified. Accordingly, the cloning and characterization of this gene in the rat have been the subject of this research. The gene has seven exons and six introns and is approximately 10kb in size. The organization and nucleotide sequence of the coding exons are similar to those of the corresponding human and mouse genes, which are the only other mammalian FBP genes cloned. However, the amino acid sequence of the rat FBPalpha is less homologous, having 48% identity with the published sequences for all the mammalian FBP isoforms. A finding not previously reported is the expression of two FBPalpha transcripts in the kidney that differ in the length of the 5' untranslated sequences, as determined by rapid amplification of cDNA end-polymerase chain reaction amplification (RACE-PCR). The brain expresses a single transcript intermediate in size between the two transcripts expressed in the kidney. The kidney transcripts are encoded by the same gene and appear to be regulated either from two independent promoters or from a single promoter in association with alternative RNA splicing.