J. Biol. Chem., Vol. 265, Issue 14, 8252-8258, 05, 1990
Structure and chromosomal location of the rat ribophorin I gene
A Behal, K Prakash, P D'Eustachio, M Adesnik, DD Sabatini and G Kreibich
Department of Cell Biology, New York University School of Medicine, New York 10016.
Ribophorin I is a type I transmembrane glycoprotein characteristic of the
rough portions of the endoplasmic reticulum where it is thought to play a
role in the cotranslational insertion of nascent polypeptides. A rat
ribophorin I cDNA was used to isolate four overlapping genomic clones from
a rat EMBL3 genomic library. Restriction mapping, Southern blotting, and
DNA sequencing showed that these clones, spanning approximately 21
kilobases of chromosomal DNA, include the entire ribophorin I gene, as well
as 15 kilobases (kb) of upstream sequences. Southern blotting analysis of
DNA from a panel of mouse-Chinese hamster cell hybrids demonstrated that
the ribophorin I gene is located on mouse chromosome six. The ribophorin I
gene contains 10 exons, seven of which encode the luminal domain of the
polypeptide. Exon 8 encodes the trans-membrane domain and small portions of
the flanking luminal and cytoplasmic domains. Exons 9 and 10 encode the
remainder of the cytoplasmic domain, and the latter includes the
3'-untranslated portion of the mRNA. Six closely spaced transcription start
sites located 3 to 24 base pairs upstream from the initiation codon were
identified by primer extension analysis and S1 mapping. The sequence of a
1.3-kb region upstream of the cap sites was determined and found to contain
three GC-rich potential Sp1-binding sites beginning at -14, -24, and - 91
base pairs (bp), two octamer-like sequences at -233 and -1248 bp, and a
CAAT-like box at -41 bp. The possible roles of these elements in regulating
expression of the ribophorin gene in all cells and in differentiated cell
types characterized by a well developed rough endoplasmic reticulum is
discussed.