ISOLATION AND CHARACTERIZATION OF A CDNA-ENCODING A XENOPUS IMMUNOGLOBULIN BINDING-PROTEIN, BIP (GRP78)

We have isolated a full length cDNA clone encoding a Xenopus laevis im munoglobulin binding protein (BiP; also called glucose-regulated prote in or grp78). The BiP cDNA sequence includes an open reading frame of 1,965 bp encoding a 655 amino acid protein with an N-terminal hydropho bic leader sequence and a C-terminal KDEL tetrapeptide which has been found in other lumenal proteins of the endoplasmic reticulum. The 3'un translated region contains a polyadenylation and an adenylation contro l element (ACE) as well as a putative mRNA instability sequence. The X enopus BiP amino acid sequence displayed high identity with BiP from o ther vertebrates including chicken (91.3%), rat (90.7%), and human (89 .9%). Northern hybridization analysis demonstrated that BiP mRNA was p resent constitutively in the Xenopus A6 kidney epithelial cell line an d that BiP mRNA levels could be enhanced by treatment of the cells wit h galactose-free media, 2-deoxyglucose, 2-deoxygalactose, glucosamine, tunicamycin, heat shock, dithiothreitol, and the calcium ionophore, A 23187. Finally, while BiP mRNA was detected in all of the adult tissue s examined, the relative level of BiP mRNA differed dramatically betwe en organs. For example, relatively high levels of BiP mRNA were detect ed in liver with moderate levels in testis, ovary and heart and reduce d levels in eye and muscle tissue. Copyright (C) 1997 Elsevier Science Inc.