Abstract
Protein CHI is a defective human .gamma.3 H chain immunoglobulin with a deletion encompassing a portion of the variable and constant regions. Joining of the 2 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. A 45 nucleotide fragment is probably the repetitive unit coding for the extra fragment.