This gene locus controls recovery from viremia and leukemia induced by Friend virus (FV). This dominant allele is found in C57BL/6J, C57BL/10, and 129P2/OlaHsd strains and allows for recovery from both viremia and leukemia in H2b mice. Recovery from viremia only is seen in H2a mice. This allele produces a full length mRNA transcript (including exon 2) that encodes for a protein with potent anti-viral activity.