Abstract
The int-1 gene is often activated by proviral insertion in mouse mammary tumors. Direct evidence for the normal function of this gene and its role in tumorigenesis has therefore been lacking. To examine possible biological effects of int-1 activation in in vitro cell systems, we have constructed recombinant molecules of genomic int-1 DNA, transcriptionally activated by retroviral promoters. Transfection of these constructs into cuboidal RAC311C mammary cells leads to morphological transformation of the cells and rapid tumorigenicity.