A replication-competent, endogenous retrovirus from an aged DBA/2 mouse contains the complete env from Emv-3 and a novel gag partially related to AKT-8.

We previously described an endogenous murine retrovirus, rv-DBA/2aged, isolated from an aged DBA/2 mouse. The previous report showed that a recombination which resulted in the replacement of Emv-3 gag sequences with gag sequences homologous to those found in the AKT-8 virus had taken place. This recombination allowed production of a competent virus from the defective Emv-3 locus. However, the extent of replacement of Emv-3 gag was not known. We report here the entire sequence for the gag gene of rv-DBA/2aged as well as the previously unsequenced 3' end of the Emv-3 gag gene. These data demonstrate that while sequences homologous to the entire gag gene fragment found in AKT-8 are represented in rv-DBA/2aged, the remainder of rv-DBA/2aged gag is not derived from Emv-3 but is a unique gag sequence. Furthermore, a complete comparison of env sequences shows that the env of rv-DBA/2aged is derived entirely from Emv-3. Additional data suggest that the recombination which led to production of the rv-DBA/2aged virus may be a common event in aging DBA/2 mice. Finally, comparison of the new sequences of Emv-3 with those of the Akv virus (also designated AKR-623 and Emv-11) and Emv-1 shows that this endogenous virus locus is very closely related to the other Emv loci at the nucleotide sequence level.