%0 Journal Article %A Tzavaras, Theodore %A Stewart, Monica %A McDougall, Ann %A Fulton, Ruth %A Testa, Nydia %A Onions, David E. %A Neil, James C. %T Molecular cloning and characterization of a defective recombinant feline leukaemia virus associated with myeloid leukaemia %D 1990 %J Journal of General Virology, %V 71 %N 2 %P 343-354 %@ 1465-2099 %R https://doi.org/10.1099/0022-1317-71-2-343 %I Microbiology Society, %X The GM1 strain of feline leukaemia virus (FeLV) was isolated from a naturally occurring case of myeloid leukaemia and induces severe haematopoietic abnormalities, including myeloblastic leukaemia, on inoculation into cats. Molecular clones of FeLV-GMl proviruses were obtained and studied by restriction enzyme mapping, blot hybridization and partial DNA sequence analysis. Two types of clone were isolated; the first was a replication-competent FeLV of subgroup A, resembling other low or minimally pathogenic FeLV-A isolates; the second was replication-defective with extensive deletions and mutations in gag and pol, although it has an intact env gene of subgroup B phenotype. Large segments of the defective proviruses, from the 5′ leader sequence upstream of the gag gene to the 5′ half of the env gene, show structural hallmarks of endogenous FeLV-related proviruses. Infectious FeLV-GMl viruses recovered after transfection were tested for their leukaemogenic potential in newborn cats. Early polyclonal myeloproliferative changes were observed in cats inoculated with FeLV-A/GMl alone, although these were more pronounced in animals receiving the full FeLV-AB/GMl complex reconstituted by cotransfection of the defective virus FeLV-B with its FeLV-A helper. Analysis of viruses in the bone marrow showed that replication of the subgroup B component is delayed and restricted to a proportion of cats. Most of the infected cats developed persistent abnormalities of haematopoiesis and one progressed to disseminated myeloid leukaemia. The defective recombinant FeLV-B/GMl appears to play an indirect but important role in myeloid leukaemogenesis. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-71-2-343