HostControl ofEndogenous MurineLeukemia VirusGeneExpression: Concentrations ofViral Proteins inHIigh andLowLeukemiaMouseStrains

Twoofthemajormolecular components ofmurineleukemia virusparticles, theinternal protein (p30) andtheenvelope glycoprotein (gp69/71) havebeen measuredinthespleens ofnormal,6-to10-week-old miceofvarious inbredstrains andcrosses. Bothproteins weredetected invirtually allmice.Extracts ofhighleu- kemia,highmurineleukemiavirusstrains (AKR,C58, PL)showedhighlevels ofbothproteins; extracts ofother strains usually showedlowerlevels. Ofparticular interest, however, weretheexceptions tothesegeneral observa- tions: (1)Verylittle gp69/71 couldbedetected inspleens of BALB mice,andthistrait wasdominantincrosses with AKR andDBA/2,bothofwhichexpress a highlevel of gp69/71. Thymus-deficient BALB/c-nu/nu (nude) mice, incontrast, showeda higherconcentration ofgp69/71 typical ofotherlowleukemia strains, suggesting thatthe virtual absenceoftheprotein innormalBALB/cmice mayresult fromimmunologic suppression. (2)WithC57L, C57BL/l0Sn, andC57BL/6 strains theconcentration ofp30 waslower, insomecasesmuch lower, thanwouldbeex- pected fromtheconcentration ofgp69/71. (3)DBA/2mice showedhighlevels ofgp69/71, 10-fold greater thanthat ofp30,whereascongenic DBA/2-Fv-lb miceshowedthe opposite pattern. (4)Miceof129-Gix- strainshowedno detectable levels ofeither p30orgp69/71 proteins, although thecongenic 129(Gix+) showedappreciable levels ofboth. Theabsence oftheseproteins in129-Gix- miceisareces- sivetrait, asF1hybrids withAKR andDBA/2showed appropriate levels ofbothproteins. Itisconcluded that expression ofviral p30andgp69/71 proteins inmiceisnot coordinately linked andthatexpression iscomplex, being influenced byseveral genes,including Gv-1,H-2,Fv-I, andprobably still others. Evidence frommanysources, culminating withthedemon- stration that clonal lines ofvirus-free mouseembryo cells can beinduced toyield type-C RNAviruses, hassuggested that thegenetic determinants ofmurine leukemia viruses (Mu- LV)arepresent asheritable components inallmousecells (1-5).