Recombinants between temperature-sensitive mutants of rauscher murine leukemia virus and BALB:virus-2: genetic mapping of the Rauscher murine leukemia virus genome

Mutants of murine leukemia viruses and retroviral replication

The analysis of retroviral mutants has played a critical role in the development of our understanding of the complex viral life cycle. The most fundamental result of that analysis has been the definition of the replication functions encoded by the viruses. From a biochemical examination of a particular step in the life cycle it is difficult to determine, for example, whether that step is catalyzed by a viral or a host enzyme; but the isolation of a viral mutant defective in that step can firmly establish that a viral function is involved. In this way many facts about the viruses have been established. We know that reverse transcriptase is encoded by the virus; that RNAase H and DNA polymerase activities reside on the same gene product; that processing of many precursor proteins is mediated by a viral proteinase; and that establishment of the integrated provirus requires a viral protein. The list of functions mediated by viral enzymes has largely been defined by the mutants isolated and studied in various laboratories. The second significant result of the studies of viral mutants has been the assignation of the replication functions to particular viral genes, and then more specifically to particular domains of these genes. Mutants and viral variants have been essential in the determination, for example, that the gag protein is the critical gene product for the assembly of a virion particle; that the env protein is the determinant of species specificity of infection; or that the LTR is a major determinant of tissue tropism and leukemogenicity. The subdivisions of functions within a given gene have similarly hinged on mutants. Genetic mapping was needed to establish that P30 is the most important region for assembly; that the proteinase and integrase functions reside, respectively, in the 5' and 3' portions of the pol gene; and that the glycosylated gag protein is dispensable for replication. A third important area of knowledge has depended heavily on viral mutants: the determination of host functions and proteins that interact with viral proteins. Variant viruses with altered or restricted host ranges serve to define differences between pairs of different host cells, and the mapping of the viral mutations serves to define the viral protein important in that interaction with the host. These studies are only in their infancy, but it is clear that substantial efforts will be made to further analyze these host functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Different recombinant murine leukemia viruses use different cell surface receptors

Retroviruses can be grouped by viral interference measurements into classes which use common cell surface receptors. We previously tested a large number of isolates of mink cell focus-inducing (MCF) murine leukemia viruses (MuLVs), and reported that all of them share a distinct receptor on NIH/3T3 cells (A. Rein, Virology 120, 251, 1982). We now extend this generalization to several additional recombinant isolates, including two (SL3-2 and GPA-V2) which would not be considered MCFs on the basis of host-range data. We note the superiority of interference tests, based on positive, unambiguous data, over host-range tests for virus classification. We also show that in contrast to the MCFs, which are all derived from ecotropic MuLVs, a recombinant derived from wild mouse amphotropic MuLV (S. Rasheed et al., Int. J. Cancer 29, 345, 1982) uses a unique receptor on NIH/3T3 cells. This suggests that (a) mouse cells contain more than one type of endogenous env sequence; and (b) there is some specificity in the generation of recombinants, since ecotropic MuLVs appear to give rise only to MCFs, while amphotropic MuLV has generated a distinct type of recombinant. It also represents a second case (in addition to the MCFs) in which an env gene recombinant is more pathogenic than its exogenous parent. We also show that xenotropic MuLV does not interfere with MCFs in NZB mouse cells; thus, despite the close homology between MCF and xenotropic env sequences, the gp70 of xenotropic MuLV appears to have no detectable affinity for the MCF receptor.

Applications of Oligonucleotide Fingerprinting to the Identification of Viruses

This chapter focuses on applications of oligonucleotide fingerprinting to the identification of viruses. Fingerprinting is a technique by which oligonucleotides, produced by cleavage of RNA molecules with specific ribonucleases, are separated in two dimensions. It is a definitive method of identifying RNA viruses according to their genotypes. It is not subject to the problems of antigenic drift or antigenic convergence that complicate serological identification. Furthermore, it provides a semiquantitative means of following the evolution of viral genomes in nature. Because all regions of the genome are represented by the large diagnostic oligonucleotides, a survey of the total genomic changes can be monitored. Fingerprinting has two limitations as a diagnostic tool. First, although highly definitive, fingerprinting is not as rapid or inexpensive as serological techniques and cannot be as easily scaled up for routine identification of a large number of samples. Second, the evolutionary range of fingerprinting is short and relationships may not be evident for isolates of rapidly evolving viruses obtained over long intervals. However, these limitations are not large, compared to the full benefits offered to the virologist by the fingerprinting method.

Isolation and characterization of new ecotropic murine leukemia viruses after passage of an amphotropic virus in NIH Swiss mice

Amphotropic murine leukemia viruses (MuLV-A) cause mainly lymphoma in newborn inoculated NIH Swiss mice after a long latent period of 6-12 months. Rarely, however, about 1% of the inoculated mice develop hind limb paralysis and progressive central nervous system disease. The biological properties and RNase T1-resistant oligonucleotide fingerprints of the recovered viruses from tissues of both lymphomatous and paralyzed mice inoculated with MuLV-A were analyzed. These results indicate that serial in vivo passages of MuLV-A in NIH Swiss mice lead to generation of new MuLVs of both amphotropic and ecotropic host ranges. The recovered amphotropic viruses are highly lymphomagenic and are recombinants of MuLV-A-specific oligonucleotides and endogenous mouse sequences. The ecotropic viruses fall into two groups: (1) recombinants of MuLV-A genes and NIH Swiss mouse viral or cellular sequences and (2) new ecotropic viruses with oligonucleotide fingerprints not related to any of the known MuLVs. The naturally occurring ecotropic MuLVs of the wild mice produce both lymphoma and paralysis in NIH Swiss mice. The viruses recovered from in vivo passages are mainly of ecotropic host range although dual-tropic virus activity is occasionally seen in the spleens but not in the brains or spinal cords of the lymphomatous or paralyzed mice. Oligonucleotide fingerprinting of the recovered MuLV-Es from paralyzed mice are identical to the input MuLV-Es, indicating that the parental MuLV-E alone, without recombination, is responsible for the paralytic disease.