Figure 3.

Nucleotide sequences of V_H genes in hybrid loci expressed by hybridomas from BP2 (B29 promoter) transgenic mice (above solid line) and CPM (enlarged leader intron) transgenic mice (below solid line). Only those sequences containing at least one mutation are shown. The reference sequence is that of the unmutated 3665V_H gene. Hybridoma names are listed to the left of each sequence. Dashed lines indicate sequence identity. Mutations are shown explicitly. Only those codons in which mutations were observed, as well as junctional codons, are shown. Recurrently observed nucleotide changes at codons 58 and 59 are indicated in bold. The rare junctional codons of the 36-65V_H transgene are underlined. Codons are numbered sequentially from the mature amino terminus, and the location of complementarity determining regions (CDR) are shown. At codon 58, the recurrent mutation (ACT→ ATT) results in a change from threonine to isoleucine, demonstrated to increase affinity for Ars two- to threefold (27). A variety of amino acid substitutions have been recurrently observed at codon 59. A change from lysine to threonine (AAG→ ACG), observed in two enlarged leader intron hybrid loci, increases affinity for Ars two- to fourfold (27). The lysine to asparagine mutation (AGG→ AGC) observed at this position in 3 BP2 hybridomas and 1 CPM hybridoma is recurrently observed, but its effect on Ars affinity has not been tested.