Une minorite des lymphomes thymiques induits chez le rat par un virus des radioleucoses murines presente une insertion a proximite de c-myc, et une majorite un nouvel ARN polyadenyle non viral

Thymic lymphomas were induced in rats either with the cell culture-propagated radiation leukemia virus complex, RadLV/VL₃, or with a molecularly cloned isolate, RadLV/VL₃ (T + L +). Four of thirty lymphomas, that were examined for rearrangements of the c-myc domain, displayed alterations in the vicinity of the c-myc gene, compatible with the idea of proviral integration. One of the tumours was investigated further, and was shown to contain a full length-proviral insert upstream of c-myc. Eight of nine lymphomas, that were investigated with respect to RNA expression, contained a novel polyadenylated RNA which could be detected with a molecular probe derived from the U5 portion of the retroviral long terminal repeat, but not with probes derived from the U3 portion or from the whole retroviral genome. These findings suggest that a RadLV/VL₃ (T + L +) provirus can induce or activate RNA synthesis from c-myc by an enhancer mechanism, and from another cellular gene by a promotion mechanism.