Loss of APOBEC3 gene enhances sexual transmission of LP-BM5 virus. Age and weight-matched WT, mA3+/-, and mA3-/- male (♂) mice on C57BL/6 background (n = 5) were inoculated with LP-BM5 virus via the IP route. Four weeks after infection, mice were mated for 6 days (normal estrus cycle in laboratory mouse) with age and weight-matched WT, mA3+/-, and mA3-/- female (♀) mice on C57BL/6 background (n = 3). Female mice were removed from their male partners, housed separately, and pregnancy status determined to ensure mating. Male mice were sacrificed upon removal of female partners (five weeks post infection). All female mice were bled on day 12 following mating to obtain peripheral blood mononuclear cells (PBMCs) and then sacrificed. Upon necropsy, the testes and spleen were collected from male mice and spleen from female mice. DNA was extracted from all samples. Rate of male mice infection was examined by examining level of viral DNA present in testes (A) and spleen (B). Rate of virus transmission was determined by evaluating level of viral DNA present in spleen (C to E) and PBMCs (F to H) of female mice of different genotypes mated to male mice of different genotypes. Side-by-side comparison of sexual virus transmission from WT, mA3+/-, or mA3-/- infected male to a WT female is shown for spleen (I) and PBMCs (J). Error bars are standard error; * is significance with p value equal or less than 0.05; and ** is significance with p value equal or less than 0.01. Experiments were performed at least three different times with similar results. ♂ = male, ♀ = female.