Identification of two allelic IgG1 C(H) coding regions (Cgamma1) of cat.

Two types of cDNA encoding IgG1 heavy chain (gamma1) were isolated from a single domestic short-hair cat. Sequence analysis indicated a higher level of similarity of these Cgamma1 sequences to human Cgamma1 sequence (76.9 and 77.0%) than to mouse sequence (70.0 and 69.7%) at the nucleotide level. Predicted primary structures of both the feline Cgamma1 genes, designated as Cgamma1a and Cgamma1b, were similar to that of human Cgamma1 gene, for instance, as to the size of constant domains, the presence of six conserved cysteine residues involved in formation of the domain structure, and the location of a conserved N-linked glycosylation site. Sequence comparison between the two alleles showed that 7 out of 10 nucleotide differences were within the C(H)3 domain coding region, all leading to nonsynonymous changes in amino acid residues. Partial sequence analysis of genomic clones showed three nucleotide substitutions between the two Cgamma1 alleles in the intron between the CH2 and C(H)3 domain coding regions. In 12 domestic short-hair cats used in this study, the frequency of Cgamma1a allele (62.5%) was higher than that of the Cgamma1b allele (37.5%).