Identification of two allelic IgG1 Ch coding regions (Cγ1) of cat

Two types of cDNA encoding IgG1 heavy chain (γ1) were isolated from a single domestic short-hair cat. Sequence analysis indicated a higher level of similarity of these Cγ1 sequences to human Cγ1 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 Cγ1 genes, designated as Cγ1a and Cγ1b, were similar to that of human Cγ1 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 Ch3 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 Cγ1 alleles in the intron between the Ch2 and Ch3 domain coding regions. In 12 domestic short-hair cats used in this study, the frequency of Cγ1a allele (62.5%) was higher than that of the Cγ1b allele (37.5%).