Structure of gastrin gene and regulation of its transcription termination

Abstract

The complete nucleotide, sequences of cDNAs coding for bovine and feline preprogastrin have been determined. The gastrin mRNA of each animal encodes a preprogastrin of 104 amino acids consisting of a signal peptide, a prosegment of 37 amino acids, and a gastrin 34 sequence, followed by a glycine (the amide donor). The cleavage following a pair of lysine residues yields gastrin 17. We found that pairs of arginine residues flanking gastrin 34, the typical processing the site sequence of all other preprogastrins and many peptide hormones, were arginines in the bovine preprogastin, but the first basic amino acid pair had changed to Arg-Trp (57-58 residues) instead of Arg-Arg in the feline preprogastrin. Comparison of these amino acid and nucleic acid sequences with published mammalian sequences showed extensive homology in th coding (63 to 73%) and in the untranslated regions (67 to 89%). We have isolated genomic clones that encode the monkey and sheep gastrin, and characterized their restriction maps. The nucleotide sequence of the 3`` flanking regions of the two genes as well as mouse gastrin gene were analyzed. The terminator-like sequence of monkey gastrin gene for RNA polymerase II, when compared to the previously known human terminator $U_5AU_4AU_4AU_5$, was identical except that the last nucleotide was changed from U to A. To identify the termination element in mouse and sheep gastrin genes, we employed a in vivo transiently expressing system. The potential Z-DAN forming element, GT-repeat sequence at the 3`` flanking region of mouse gastrin gene, acted as a transcription terminator. When the element was deleted from its site, the effect of termination disappeared perfectly. When the element was artificially inserted into the 3`` flanking region of sheep gastrin gene which had not shown any transcription termination, the effect of termination newly appeared. The GT-repeat element responsible for transcription termination functioned with orientation-dependent...