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Publisher Summary This chapter discusses the restriction of murine leukemia viruses by Fv-1—that is, a model for studying host genetic control of retroviral gene movement and leukemogenesis. The Fv-1 locus is known as a genetically determined host-resistant factor to murine viral leukemogenesis. With the development of an in vitro cell culture system to define the host range of different murine leukemia virus isolates, this genetic factor was found to have two kinds of alleles, Fv-1n and Fv-lb, which specify resistance to B-tropic and N-tropic viruses, respectively, in a dominant fashion. The locus has been mapped adjacent to the Gpd gene in chromosome 4 of the mouse. It is significant that all mouse strains, wild mice included, have an Fv-1 locus and that all naturally occurring or chemically induced endogenous ecotropic murine leukemia viruses are susceptible to restriction by one allele or another. The chapter summarizes the basic facts that are important for further investigation of the molecular mechanism of Fv-1 restriction.

Publisher Summary This chapter discusses the analyses of molecular clones of an endogenous ecotropic virus of BALB/c mice, WN1802N, to identify possible changes that occur in the long terminal repeat (LTR) region. In these analyses, covalently-closed circular DNA intermediates were isolated from cell cultures 48 hours post-infection and cloned by constructing Hin dIII recombinants with Charon 9 bacteriophage. The DNA of 15 independent isolates was first analyzed by Hin dIII restriction and endonuclease digestion, agarose gel electrophoresis, and Southern blot hybridization. Seven of the clones (λWN7, λWN12, λWN26, λWN30, λWN36, and λWN41) have an insert size that corresponds approximately to the complete MuLV genome containing two LTRs. There are four different size LTRs in this population of clones. The most abundant size class is 520 bp and it is probable that this is the size of the endogenous provirus LTR. Seven of these are infectious. There are three isolates with a 600-bp LTR, one of which is infectious, one with 570 bp, and one with 670 bp. Neither of these last two are infectious, but it is yet to be determined whether this is related to the LTR.

Publisher Summary Radiogenic myeloid leukemia in RFM/Un mice is a potentially valuable model system to study specific chromosomal rearrangements of retrovirus genes. One of the key aspects of this system is that infection by an endogenous virus is strongly restricted; therefore, an extracellular spread of the virus is not likely to play a role in the formation of additional integrated viral genomes, as is the case in other well-studied murine retrovirus models. The role RFV plays in radiogenic myeloid leukemia is uncertain. As with other endogenous ecotropic retroviruses, the virus does not transform cells in culture and does not appear to accelerate leukemogenesis in vivo . A downstream promotion model for leukemogeneis by avian leukosis virus does provide an attractive hypothesis for the involvement of RFV in the myeloid leukemia. Studies indicate that there is a single locus for the inducible ecotropic provirus that resides on chromosome 5. The myeloid leukemic cell line clearly has additional copies of the ecotropic provirus.

Publisher Summary This chapter describes an application of the reversed-phase column chromatographic system (RPC); presents general procedures for preparing tRNA and aminoacyl-tRNA synthetases from the tissue and for preparing labeled aminoacyl-tRNA suitable for the chromatographic analysis; and demonstrates the analysis of iso-accepting tRNAs of an amino acid with a sample size in the range of 1 A260 unit of mixed tRNA. This method is very useful, especially in cases, where the source of material for preparing tRNA is limited, such as tissue culture cells and small animal organs. The sensitivity of this method is facilitated by the availability of radioactive amino acids with high specific activity. The isoaccepting peaks of an aminoacyl-tRNA are sufficiently well resolved in the column that quantitative comparative studies can be done by cochromatography of two samples with different labels. Because, the size of the tRNA sample is small, it becomes very important that artificial modifications of amino-tRNA should be prevented. The profiles of isoaccepting tRNAs for individual amino acids are much different between the mammalian and the bacterial sources.