Spontaneous somatic frameshift mutation in a mouse myeloma

Abstract

The precise alteration in the protein amino acid sequence of the heavy chain of IF3, a spontaneously-arising mutant of the P3K line of the mouse myeloma MOPC 21, has been determined. The secreted immunoglobulin of IF3 was more basic than wild type, and its heavy chain was smaller. The primary structure of IF3 heavy chain was studied by isolating all its CNBr fragments and selected tryptic peptides. The sequence of the mutant heavy chain was identical to wild type in the first 340 residues. The sequence of the remaining 14 residues of the mutant heavy chain was unique for immunoglobulins. The mutant sequence is related to the wild type by a two-base deletion in the coding sequence of the gene for MOPC 21 heavy chain. This explanation, a −2 frameshift, allows a unique sequence of 47 bases, that includes the bases deleted in IF3, to be deduced for MOPC 21 heavy-chain mRNA, and predicts the premature “ochre” termination for IF3.