Mutant Sl alleles of mice affect susceptibility to Friend spleen focus-forming virus.

Mice of genotypes S1/S1(d), S1/+, and S1(d)/+ (but not S1(T)/S1(T) or S1(T)/+) were resistant to spleen focucs-forming virus. The "environment" in which hemopoietic target cells for this virus develop was not conducive for infection or focus formation, or both, but the target cells were not altered directly. The same genes appear to regulate hemopoiesis and leukemogenic transformation.