Minus-strand annealing and transfer activity of NCp7 in the absence or presence of HIV-1 SP2 added in trans. (A) Primary sequence of NCp9. The zinc coordinating residues (Cys and His) are shown in gray. The arrow indicates the PR cleavage site. The final products NCp7 (55 residues) and SP2 (16 residues) are separated by lines placed at the bottom or the top of the sequence. (B) Bar graphs. 33P-labeled DNA 128 was incubated with RNA 148 for 60 min in the absence (No, open bars, lanes 1, 8, 15, and 22) or presence of increasing concentrations of NCp7 as follows: NCp7, closed bars, lanes 2 to 7; SP2, light gray bars; lanes 9 to 14; NCp7+SP2 in trans, hatched bars, lanes 16 to 21; NCp9, dark gray bars, lanes 23 to 28). The % annealed product (upper series of bar graphs) or % transfer product (lower series of bar graphs) was plotted as a function of protein concentration. Note that in each NCp7+SP2 reaction, the two proteins were present in equal concentrations.