A comparative study of the avian reticuloendotheliosis virus: relationship to murine leukemia virus and viruses of the avian sarcoma-leukosis complex.

Reticuloendotheliosis virus (REV) with several related viruses comprises a group of C-type, avian RNA tumor viruses which is distinct from the avian leukosis-sarcoma virus (ALSV) complex. The emphasis of the present investigation has been on the comparison of the properties of REV with those of a model mammalian RNA tumor virus, murine leukemia virus (MuLV), and with those of the ALSV.The structure and pathway of maturation of these viruses has been examined using electron microscopy. Conclusions derived from this work indicate that while the immature particles of REV can be morphologically distinguished from both MuLV and ALSV, the mature REV particle is very like that of MuLV and quite different from that of ALSV.The properties of the purified DNA-polymerase of these viruses were analyzed with the following significant findings: 1) Unfrozen, purified disrupted REV, but not purified REV-DNA-polymerase is enzymatically active using natural viral RNA as template-primer; 2) the DNA-polymerase copurifies with an RNase-H activity which probably resides on the same polypeptide; 3) the size of the DNA-polymerase-RNase-H complex is indistinguishable from that of the MuLV, a single polypeptide of 84,000 daltons; 4) the divalent cation preference of the REV-DNA polymerase, like that of MuLV, but unlike that of ALSV, is for Mn²⁺; and 5) serological cross-reaction between the DNA-polymerase of REV and ALSV could not be demonstrated.Apart from these structural and biochemical analogies, no direct relationship between REV and MuLV has been established. Infectivity of REV in two strains of mouse cells could not be demonstrated. Immunodiffusion tests for reaction of purified, disrupted REV with antisera specific for ALSV structural components and for the interspecies specific reaction characteristic of mammalian RNA tumor virus p 30 protein were uniformly negative. After consideration of all the available data, it seems that the REV must be considered a distinct group of avian RNA tumor viruses with significant structural similarities to mammalian viruses, but nonetheless differing antigenic determinants.