Isolation and characterization of a cDNA encoding porcine gastric haptocorrin

A cDNA encoding the gastric haptocorrin was isolated from a porcine gastric mucosal lambda gt11 cDNA library using oligonucleotide probes. The 1.4-kb cDNA contains a 1.25-kb open reading frame and 178 nucleotides of 3' noncoding region. Although no initiator methionine is present, primer extension analysis indicated that the transcription initiation site is only 100 bp upstream of the 5' end of this clone. Northern blot analysis showed that a single mRNA species of 1.6 kb exists in hog gastric mucosa. There was no cross-hybridization between this cDNA and the mRNA for haptocorrin in rat submaxillary gland or gastric RNA by Northern blot analysis. This lack of cross-reactivity was also seen on Southern blots, where cow, sheep and dog but neither rat nor mouse genomic DNAs showed cross-hybridizing bands. Comparison of the deduced amino acid sequence of this cDNA with that previously reported for rat intrinsic factor [Dieckgraefe, B.K. et al. (1988) Proc. Natl Acad. Sci. USA 85, 46-50] showed considerable similarity, suggesting that these cobalamin-binding proteins may have a common evolutionary origin.