Functional and pseudogenes are similarly organized and may equally contribute to the extensive antibody diversity of the IgVHII family.

Eleven germ-line immunoglobulin VH genes have been isolated from a BALB/c genomic library, using a cDNA probe specific for the GAT/NPa variable region. Restriction fragments of all genes were sequenced: two over 800 bp, covering signals of the 5'- and 3'-non-coding regions, three encompassing the complete coding region and part of the 5', the remaining sequences covering most of the V coding region. All sequences pertained to the VHII family, and were compared with the other 13 homologous genes already published. Characteristic features defining the family are clearly visible all along the sequences analyzed, including the 5'-non-coding region, the leader fragment and the intron organization. About half of the compared genes have pseudogene characteristics, defined either by a stop codon in the coding region or the lack of an initiator codon in the leader segment. Analysis of the replacement mutations, as compared with silent ones, indicate that they are highly clustered in complementarity determining regions, for both the functional and the pseudogenes, suggesting that all genes have been submitted to similar selective pressure, and that the pseudogene repertoire may be actively used, by recombination and/or conversion process. Signals that regulate transcription are highly conserved through the family barriers. The VHII group is the largest Ig V genes family, with extreme sequence divergences reaching 22% nucleotide differences. As no two genes were found identical out of the 24 members compared, and as two genes were found to differ by as little as three nucleotides, it seems that the previous estimate of 60 members might be much too low.