Possible origin of murine AIDS (MAIDS) virus: Conversion of an endogenous retroviral p12(gag) sequence to a MAIDS-inducing sequence by frameshift mutations

The murine AIDS (MAIDS) virus has a unique sequence in its p12(gag) region, which is responsible for MAIDS development. A transcript hybridizing with this sequence is expressed in normal C57BL/6 mice. The transcript, designated Edv, has been previously cloned and sequenced (Y. Kubo, Y. Nakagawa, K. Kakimi, H. Matsui, K. Higo, L. Wang, H. Kobayashi, T. Hirama, and A. Ishimoto, J. Gen. Virol, 75:881-888, 1991). Compared with the nucleotide sequence of the helper LP-BM5 ecotropic virus, the pathogenic replication-defective MAIDS virus has a 16-bp deletion and a 1-bp insertion in the 5' and 3' regions of the p12(gag) sequence, respectively, and the Edv transcript contains only a 3-bp deletion. Therefore, the amino acid sequence of the defective MAIDS virus p12(gag) region is not homologous to that of the helper virus and the Edv transcript because of the frameshift. To determine whether the amino acid sequence resulting from the frameshift is critical for MAIDS development, we constructed chimeric viruses that contained the p12(gag) regions of the helper virus and the Edv transcript, respectively, with and without the same frame as the defective MAIDS virus by the artificial frameshift mutations. The mutant viruses with the frameshift mutations induced MAIDS in inoculated mice, but the viruses without the mutations did not. These results suggested that the MAIDS virus was generated by frameshift mutations in the p12(gag) region of Edv or a related sequence.