Native analysis of virion-associated RNA. Mutant or wild-type virus was purified by sucrose gradient ultracentrifugation. Virion RNA was then extracted from lysed particles by protease K digestion followed by phenol chloroform extraction. RNA was run under non-denaturing conditions at room temperature. Membranes were analyzed with an SIV specific probe as described in Materials and Methods. A. Non-denaturing Northern analysis of the SD2 variant in conjunction with compensatory mutants in the DIS, CA, and p6. B. Non-denaturingNorthern analysis of the SD2 variant in conjunction with compensatory mutants in the DIS and in the NC protein.