MAC-1, a new genetically transmitted type C virus of primates: "low frequency" activation from stumptail monkey cell cultures.

A new class of endogenous primate type C virus has been isolated from a continuous tissue culture line of Macaca arctoides cells by co-cultivation with a human cell line. The virus, designated MAC-1, can be transmitted to human and feline cells in tissue culture, and is unrelated, by immunological and nucleic acid hybridization criteria, to previously characterized retroviral isolates of primates. In particular, MAC-1 shows no detectable homology to the baboon type C viruses, even though viral genes related to the latter group are readily detected in M. arctoides cellular DNA. Viral gene sequences related to the MAC-1 genome are present in multiple copies (50-150 per haploid genome) in Old World primates, and are expressed in the cellular RNAs of uninfected and "virus-free" primate cells and tissues. Thus there are at least two distinct sets of genetically transmitted Old World primate type C viral genes, each of which is found in multiple copies in normal primate cellular DNA. With the description of this new retrovirus, there are now a minimum of five distinct genetically transmitted viruses of primates, three type C and type D, each represented in multiple copies in the normal cellular DNA.