Figure 4.

(a) Nucleotide sequences and (b) deduced amino acid sequences of clonally related, productive IGHV4–4DJ_H6B-Cγ2 (labelled IgG2) and -Cγ1 functional transcripts (labelled IgG1). Sequences are shown aligned with the germline, unmutated IGHV4-4 and J_H6B gene segments¹⁴ and with the 5′ end of the Cγ2 or Cγ1 exon. The location of the third complementarity-determining region of the immunoglobulin heavy chain (H-CDR3) is indicated. In (a), replacement point mutations are shown by uppercase letters, and silent point mutations by lowercase letters. In the IgV_H4 gene segment, all base substitutions are shared by both immunoglobulin (Ig) transcripts sequences, except five mutations which are located in the FR1 domain. Dashes indicate identity with the above located nucleotide sequence. RNA splice sites (5′ end of Cγ exons) are represented by asterisks. Annealing sites of the sense V_H5 FR1 and antisense Cγ PCR primers have been italicized. Differences in the nucleotide sequences between the human Cγ1 and Cγ2 exons have been underlined. Identical nucleotide sequences of the H-CDR3 and the partially shared pattern (72·2%) of base substitutions illustrate two clonally related omental cells of the B lineage which have diversified by class switch recombination event after somatic hypermutation.