Mechanism of chemical activation of expression of the endogenous ecotropic murine leukemia provirus Emv-3.
DBA/2 mice carry a single endogenous ecotropic murine leukemia provirus, Emv-3. This provirus is defective; it is very poorly expressed in young DBA/2 mice. The defect in Emv-3 is caused by a single base substitution in codon 3 of p15gag. The resulting amino acid substitution inhibits myristylation of the gag precursor and subsequent virus assembly. Despite this defect, percutaneous treatment of DBA/2 mice with the carcinogen and mutagen 7,12-dimethylbenz[a]anthracene (DMBA) induces ecotropic murine leukemia virus replication in virtually all treated mice. We hypothesized that this induction is the result of a DMBA-induced reverse mutation in codon 3 of p15gag which allows for efficient myristylation. We tested this hypothesis by isolating ecotropic viruses from DMBA-treated mice and determining the DNA sequences of selected regions of p15gag, including codon 3. In support of the above-described model, all of the viruses examined contained single nucleotide substitutions in codon 3. In addition, most of the replication-competent viruses that were sequenced appeared to result from simple mutation of Emv-3 rather than recombination with other endogenous murine leukemia viruses. These studies may provide a basis for development of a sensitive assay for the mutagenic activity of a variety of chemical carcinogens in vivo.
Mercer
J A
JA
Mammalian Genetics Laboratory, National Cancer Institute-Frederick Cancer Research Facility, Maryland 21701.
Lee
K H
KH
Nexø
B A
BA
Jenkins
N A
NA
Copeland
N G
NG
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003062:Codon / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D015683:Gene Products, gag / Q000235:genetics; D005814:Genes, Viral / Q000187:drug effects; D009052:Leukemia Virus, Murine / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D051379:Mice; D008811:Mice, Inbred DBA; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011533:Proviruses / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D012689:Sequence Homology, Nucleic Acid
D003062:Codon; D004279:DNA, Viral; D015683:Gene Products, gag; D015127:9,10-Dimethyl-1,2-benzanthracene