Opening of the TAR structure affects dimerization of HIV-1 RNAs. The cellular (A) and virion RNA (B) isolated upon transfection of cells with the original (TARm) and 5′ TAR-mutated HIV-rtTA virions (as described in Figure 3) was incubated at 37°C and analyzed on a non-denaturing Northern blot. We included TARm RNA samples that were denatured by heating at 55°C before analysis to identify the position of the viral RNAs (right lanes). The position of the monomeric and dimeric unspliced RNAs, large RNA complexes, single and double spliced RNAs, and 12-kb RNAs (*, see legend to Figure 3) is indicated. M: mock transfected cells. (C, D) The profiles of the lanes corresponding to the non-denatured RNA samples from cells (blot shown in A) and virions (blot shown in B) were analyzed with 1-D geI analysis software (ImageQuantTL). The position of the RNA monomers, dimers and complexes are indicated.