Chromosomal organization and expression analysis of two distinct genes encoding glutamine/glutamic acid-rich proteins.

GRP-Ca and GRP-Cb are two genes that encode glutamine/glutamic acid-rich proteins of the rat. These genes are very similar in structure and sequence, differing only within an approx. 90 bp segment of exon 3. We have used distinct oligonucleotide probes to unambiguously distinguish GRP-Ca and GRP-Cb gene expression. The two genes are expressed to relatively equivalent levels only in the submandibular gland. Chronic daily exposure to the beta-adrenergic agonist, isoprenaline, resulted in a statistically significant decrease in GRP-Ca expression, with no effect on GRP-Cb, in contrast with previous reports. Furthermore it was determined by PCR analysis of both submandibular-gland cDNA and genomic DNA that the GRP-Cb gene shows interanimal variability in the number of 69 bp tandem repeats found within exon 3; GRP-Cb genes were shown to contain four, five or six repeats. GRP-Ca shows no such variability, containing only five tandem repeats in all animals examined. The two genes were localized to within 450 kb of one another at q43-q44 of rat chromosome 4 using somatic cell hybrid analysis, pulsed-field gel analysis and fluorescent in situ hybridization.