Genomic and structural context of the mutations introduced in the HIV-2 leader. (A) Genomic organisation of HIV-2 and location of the mutations introduced. The DM deletion mutant has been described previously . In SM1 the first three bases in the DIS palindrome at position 420 of the HIV-2 RNA genome are substituted. In SM2 the first four bases of the Psi palindrome at position 392 of the HIV-2 RNA genome are substituted. (B) Structure of the SL-1 region predicted by previously published biochemical analyses [20, 22, 55, 56] and mfold computer modelling [57, 58. The position of the stem proposed to extend SL-1 is indicated (stem B) .