Amino acid sequences of expressed Vλ regions compared with their closest germline λ gene, 2a2. The amino acid sequences of B3VL, B3(R27aS)VL, B33VL, BUVL, 33.H11VL, and UK-4VL regions are numbered according to the system of Wu and Kabat . Amino acids are indicated by their one-letter code. Dots have been inserted to facilitate the alignment. A dash indicates sequence identity with that of germline gene 2a2. The complementarity-determining regions (CDRs) and framework regions (FRs) have been defined according to the system of Wu and Kabat . Antigen contact sites, as defined by MacCallum and colleagues , are shown by red arrows. L1, L2 and L3 are the first, second and third contact regions of the light chain respectively.