Origin of adult T-cell leukemia virus. Implication for its zoonosis.

Adult T-cell leukemia virus (ATLV) is a retrovirus infecting man. The ATLV genome consists of long terminal repeat (LTR), gag, pol, env and pX sequences and does not carry a typical v-onc gene. The function of the pX sequence is unknown. To search for the origin of ATLV, segments of the ATLV genome were hybridized to DNAs of various species. The sequences homologous to the pX region of ATLV are represented in the genomes of mouse and rat but not in other species including primates and the human. Neither the pol nor U3 sequence of LTR is conserved in any cellular DNA examined. Sequences slightly homologous to the U3R sequence are found in rabbit, chicken and Xenopus. The results suggest that the pX sequence of ATLV might have derived from rodents. Since ATLV can infect primates, rabbit and rat, ATLV might have been prevalent among a wide variety of mammals and exchanged genetic segments (zoonotic) like influenza virus. If we assume that the original host of ATLV is a rodent rather than man, the pX sequence is homologous to host cellular sequences and reminiscent of the v-onc gene although the function of the pX sequence is not clear.