In this application we will continue to study the transforming genes associated with gamma irradiation induced thymic lymphomas in C57BL/6J mice. We have reported a specific marker chromosome consisting of a translocation between chromosomes one and five was observed in 5 of 12 gamma irradiation induced thymic lymphomas. DNA from these 5 thymic lymphomas contains a novel non-ras transforming activity detected by DNA-mediated-gene-transfer using a sensitive tumorigenicity assay in nude mice to score for the presence of transforming DNA sequences. We will clone the novel transforming gene(s), using the nude mouse tumorigenicity assay to monitor the biological activity of the cloned DNA fragments. A detailed restriction endonuclease map of the oncogene(s) will be constructed. A subclone of the biologicallly active DNA fragment, consisting of single copy mouse DNA, will be used in Southern and Northern blot analysis to determine the number and arrangement of the gene(s) in the mouse genome and whether the gene(s) is expressed in mRNA. To determine the mechanism of oncogene activation in the 5 primary radiation-induced thymic lymphomas containing the marker chromosome, the five oncogenes, or relevant portions of the transforming DNA sequences, will be cloned. If the 5 genes are the same, fine detail analysis will determine the nature of the chromosomal change(s) resulting in oncogene activation. If the 5 genes are different, then cloning and DNA sequence analysis will determine the different mechanisms of oncogene activation. Finally, we will assess the timing of oncogene activation in mouse thymocytes at intervals following gamma irradiation treatment. If the activated oncogene is associated with the presence of the marker chromosome, then the polymerase chain reaction (PCR) technique will be used to detect the breakpoint of the chromosome translocation at different stages of disease. Experimental animal models have been extremely useful in gaining insights into some of the steps involved in disease progression. This study should elucidate some of the mechanisms involved in oncogene activation as they are related to the translocation of chromosomal segments, and has the potential for identifying a new oncogene(s) involved in lymphoid malignancies.