A new immunoglobulin variant: gamma3 heavy chain disease protein CHI.

Protein CHI is a defective human gamma3 heavy chain immunoglobulin with a deletion encompassing a portion of the variable and constant regions. Joining of the two pieces takes place at the beginning of an extra fragment (Fh) in the constant region where repetitive sequences are found, apparently as the result of gene duplications and/or unequal crossover between gamma genes. It is postulated that a 45 nucleotide fragment is the repetitive unit coding for the extra fragment.