Amplification and novel locations of endogenous mouse mammary tumor virus genomes in mouse T-cell lymphomas.

Endogenous mouse mammary tumor virus genomes are amplified and located in novel cell DNA sequences in many mouse T-cell lymphomas. Transplanted tumors recovered from the same mouse strain and shown to be of independent origin by chromosomal analysis, by the presence of JH immunoglobulin gene rearrangements, or by the integration patterns of exogenous Moloney MuLV genomes frequently showed similar patterns of novel mouse mammary tumor virus-containing cell DNA fragments. This process of amplification and relocation can occur within a limited number of cell generations and in C57BL/6 mice does not lead to the synthesis of mature virus-encoded proteins. In some instances, amplified mouse mammary tumor virus genomes contained novel restriction cleavage sites in the gag-pol region. The restricted time course of occurrence, lack of synthesis of mature virion proteins, and apparent site specificity indicate that this process of retrovirus amplification differs significantly from virus replication after exogenous infection.