A brain membrane protein similar to the rat src gene product.

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Abstract
A 20,000 dalton, transformation-related, rat cell membrane protein was purified to homogeneity. This protein, p20, was originally identified in preparations of defective woolly monkey leukemia virus pseudotype of Kirsten sarcoma virus. The chromatographically purified p20 was an acidic hydrophobic protein, capable of specifically binding GTP (dissociation constant = 15 .mu.M). This nucleotide binding property and other previously reported characteristics were similar to properties ascribed to the Harvey sarcoma virus src gene product. Protein p20 also appeared similar to this src gene product when immunoprecipitates of both proteins were directly compared by 1- and 2-dimensional NaDodSO4 (sodium dodecyl sulfate) gel electrophoreses. The proteins were not identical, because their tryptic maps differed. Using a competition radioimmunoassay, the concentration of p20 was measured in cells, viruses and rat tissue. Protein p20 was not encoded by rat sarcoma viruses because it was increased only slightly after Kirsten sarcoma virus transformation of rat cells and was not increased in nonrat cells transformed by the Kirsten or Harvey sarcoma virus. Of 10 rat tissues examined, p20 was found predominantly in brain, specifically in the membranes.