The predicted amino acid sequences of rat c-raf and A-raf products were subjected to homology search against other known amino acid sequences. We found that characteristic, cysteine-rich regions present in the amino-terminal halves of c-raf and A-raf products had striking homologies with the cysteine-rich regions present in protein kinase C. These cysteine-rich regions had been shown to be deleted in the activated raf products and in the catalytically active protein kinase C produced by proteolysis. These facts suggest the significance of the cysteine-rich regions of raf products as well as those of protein kinase C in the regulation of kinase activities.

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High-molecular-weight DNAs from 43 human primary tumor tissues were examined by Southern blot hybridization for possible rearrangement and/or amplification of the following protooncogenes: the c-myc, c-erbB-1, N-myc, c-mos and c-fos genes. In an adenosquamous cell carcinoma of the stomach, the c-myc and c-erbB-1 genes were found to be simultaneously amplified 5- and 30-fold, respectively. Cooperative expression of the amplified c-myc and c-erbB-1 genes might be involved in the genesis or progression of the gastric cancer.

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