THE RAT INTRINSIC-FACTOR GENE - ITS 5'-UPSTREAM REGION AND CHIEF CELL-SPECIFIC TRANSCRIPTION

A DNA segment containing the 5'-upstream region and amino terminal rea ding frame of the gastric intrinsic factor gene was cloned from rat an d its nucleotide sequence was determined. S1 mapping demonstrated that the transcription initiation site is located downstream of the second TATA-box sequence. Similar sequence motifs to those in the pepsinogen genes transcribed in gastric chief cells were found in the deduced se quence, suggesting that the rat intrinsic factor gene is transcribed i n these cells. The genes for the intrinsic factor and its homologous p rotein transcobalamin I were apparently derived from a common ancestor al gene, since the positions of their intron insertions as well as the amino acid residues are conserved. Northern blot hybridization showed that the gene for the intrinsic factor is transcribed in the stomach but not detectably in the intestine, kidney, testis, brain, heart, liv er, lung, or spleen. In situ hybridization using radioactive complemen tary RNA clearly indicated that the major transcription site in gastri c glands is chief cells. Different locations of expression of intrinsi c factor proteins in various mammals were observed previously using an tibodies: in rat parietal cells and chief cells, in mouse chief cells, and in human parietal cells. The present results clearly demonstrated the intrinsic factor mRNA mainly in chief cells of adult rats, as in mice, suggesting that transcriptional regulation of the intrinsic fact or gene is essentially the same in rodents.