Abstract
The int-1 mammary oncogene is activated by proviruses of the Mouse Mammary Tumor Virus in many different mammary tumors. We have inserted a genomic fragment containing the protein-encoding domain of the gene into the retroviral shuttle vector pZIPneoSV(X)1. After one round of virus replication we recovered recombinant proviral DNA containing a correctly spliced copy of int-1. In vitro transcription of this cDNA version of int-1 using SP6 polymerase and translation in a reticulocyte lysate yielded a protein of approximately 37,000 daltons. High expression of int-1 in NIH-3T3 cells infected with recombinant virus did not lead to morphological transformation.