To identify mRNAs with altered expression in Rous sarcoma virus (RSV)-transformed cells, we screened a chicken embryo fibroblast (CEF) cDNA library by differential hybridization. One clone, designated R1H, showed markedly elevated mRNA expression in RSV-transformed cells. Nucleotide sequence analysis indicated that R1H mRNA encodes 78-kilodalton glucose-regulated protein (GRP78). Chicken GRP78 was found to be very highly conserved in comparison with rat GRP78 (96% identity between chicken and rat amino acid sequences). In contrast to previous observations, we found that GRP78 was induced in RSV-transformed cells in the absence of glucose deprivation. When cells were grown in glucose-supplemented medium, the level of GRP78 mRNA was approximately fivefold higher in RSV-transformed CEF than in transformation-defective virus-infected or uninfected CEF. Similar changes in GRP78 protein content were also found. Using a temperature-sensitive mutant of RSV and supplemental glucose, we found a gradual increase in the level of GRP78 mRNA beginning at 4 h after shiftdown to permissive temperature. Uridine supplementation did not block the induction seen in CEF infected with a temperature-sensitive mutant. These results indicate that GRP78 is induced by p60`VS in the absence ot glucose deprivation.One approach to understanding how oncogenes induce neoplasia is to identify genes with altered expression in transformed cells. Changes in the expression of cellular genes may be relevant to phenotypic features of the transformed cell, such as uncontrolled growth, invasiveness, resistance to immune rejection, and metastatic spread. In addition, studying the signals that control the expression of such genes can provide insight into the mechanisms of action of oncogenes.We have been investigating the changes in cellular gene expression that occur in chicken embryo fibroblasts (CEF) after transformation by Rous sarcoma virus (RSV). In the initial stage in this project, we have isolated clones from CEF cDNA or RSV-transformed CEF cDNA libraries that are expressed at different levels in RSV-transformed cells compared with uninfected cells (38). It is likely that many of the mRNAs identified by this approach are regulated in normal cell growth. Altered expression Qf such mRNAs in RSV-transformed CEF may contribute to or result from altered growth processes after transformation. One such gene, designated 9E3, was found to encode a protein similar to human connective tissue-activating peptide (1, 38). In this paper we describe the isolation and characterization of another cDNA and report on the expression of this gene in RSV-transformed and normal cells. MATERIALS AND METHODSCell cultures and viruses. Secondary CEF were maintained in Ham F10 medium supplemented with 5% calf serum, 1% chicken serum, 10% tryptose pentose broth, 100 U of penicillin per ml, 50 ,ug of streptomycin per ml, and 2 pLg of * Corresponding author. amphotericin B per ml. The medium was changed every 24 h unless otherwise noted. In some experiments, glucose was added ...