FIG. 2.
The left end of the λ chromosome and expanded views of cosB and cosN. Nu1 and A, the terminase genes, lie downstream from cos. cos consists of three subsites, cosQ, cosN, and cosB. cosB contains the terminase recognition sequences R3, R2, and R1 and the IHF binding site I1. The 22-bp sequence of cosN has partial rotational symmetry (boxed) around a central point (∗), which divides cosN into cosNL and cosNR. The arrows show the positions of the nicks, N1 and N2, placed by terminase. Base pair 48,502 of the λ sequence is labeled −1.