EXPRESSED SWINE V-H GENES BELONG TO A SMALL V-H GENE FAMILY HOMOLOGOUS TO HUMAN VHIII

The sequences of 34 swine H chain V-regions expressed with either IgG, IgA, or IgM C regions in adult swine and newborn piglets are describe d and compared. Sixteen of these V-regions were cloned by using a spec ific leader primer whereas 18 were cloned by anchored PCR. According t o the operational criterion of V-H family classification, i.e., >80% D NA sequence similarity, all sequences belong to a homogeneous V-H gene family. A total of 31 additional V-H-bearing C mu clones obtained by anchored PCR from colostrum-deprived newborn piglets hybridized equall y with a probe for C mu and a pan-V-H probe. When the consensus sequen ce of the expressed swine V-H genes were compared with those of V, gen e for humans (VHI, II, III), mouse (VHI, II, III), rabbit, and chicken , swine V-H genes seem to have common ancestry with the human VHIII fa mily, rabbit V-H genes, and the single functional V, gene of the chick en. The leader peptides of all clones obtained by anchored PCR showed <1% variability, and the deduced amino acid sequences from aa4 to aa25 in all 34 clones are identical. Framework (FR)1 and FR2 are conserved whereas FR3 shows greater variability. A total of 23 of 30 J(H) seque nces were identical, suggesting preferential use of one J(H). This fre quent, putative J(H) sequence is not similar to any J(H) gene in human s. Identical genomic Southern hybridization patterns, each with 13 ban ds of differing intensity and regardless of stringency, were obtained when either a leader or a pan-specific V-H probe was used. Analyses of individual genomic bands by single strand conformational polymorphism and sequence analysis suggest that the number of VHIII-related genes in the swine genome is <20.