Murine leukemia virus morphogenesis: cleavage of P70 in vitro can be accompanied by a shift from a concentrically coiled internal strand ("immature") to a collapsed ("mature") form of the virus core.

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Abstract
Disruption of Rauscher leukemia virus (RLV) with low levels of Nonidet P-40 yielded immature cores. These cores have a diameter of about 920 .ANG., as opposed to the 1300 .ANG. diameter of RLV, possess knob-like protuberances, and contain a concentrically coiled internal strand apposed to the core shell. The 2 major polypeptide components of immature cores are p30, the 30,000 dalton group-specific antigen, and a polypeptide that has the size and antigenic characteristics of P70, the 70,000 dalton precursor protein of the group-specific antigens of murine leukemia virus. Disruption of RLV at high ratios of Nonidet P-40 to virus yielded mature cores. These cores have an average diameter of 850 .ANG., a smooth proteinaceous perimeter and a collapsed internal strand, and they contain predominantly p30. Treatment of RLV with low levels of Nonidet P-40 for 16 h at 22.degree. C yielded cores that showed a 70% decrease in the number of immature forms and concomitant increase in the number of mature forms, a 60-90% decrease of P70, and a 30% increase in a 40,000-42,000 dalton protein. Maturation of RLV cores is probably accomplished by cleavage of P70.