Abstract
DNA from human T-cell leukemia cell lines was tested for focus-inducing activity on cultures of NIH 3T3 cells. Three leukemias yielded DNA active in this assay; restriction enzyme sensitivity of this activity indicated that similar, relatively large DNA sequences were involved. Southern blot analysis revealed conserved size classes of restriction fragments containing human repetitive (Alu) sequences in serially transfected foci derived from the active DNAs. Similar blot hybridizations with a probe specific for the human N-ras oncogene detected a 9-kilobase EcoRI fragment in all cases. DNA containing this fragment from one of the leukemias, molecularly cloned in bacteriophage lambda, displayed highly amplified focus-inducing activity in transfection assays. Thus, the N-ras oncogene appears to be active in these three human leukemias of T-cell origin.