A major genetic locus affecting resistance to infection with murine leukemia viruses. II. Apparent identity to a major locus described for resistance to friend murine leukemia virus.

The N-B locus affecting tissue culture infectivity with naturally occurring murine leukemia viruses appears to be identical to the Fv-1 locus described for sensitivity to Friend leukemia virus. Results of tissue culture studies were parallel to results of studies in vivo and indicate that the F-S virus is N-tropic and the F-B virus is NB-tropic. Inbred and partially congenic mouse strains sensitive at Fv-1 show N-type sensitivity; strains resistant at Fv-1 show B-type sensitivity. The Fv-2 locus does not appear to exert significant effect in tissue culture. Knowledge of N-B type has been useful in predicting Fv-1 sensitivity.