A general procedure for the end labeling of proteins and positioning of amino acids in the sequence.

This paper reports a procedure for the specific radiolabeling of the amino termini of proteins. By Edman degradation, a protein is protected at all lysine amino groups while retaining a free amino terminus and such a modified protein is end-labeled by an amino group-specific reagent (radioiodinated Bolton-Hunter reagent). Partial proteolyses with a variety of specific amino acid cleaving reagents generate a series of fragments which predict the location of the specific amino acids in the primary structure. The amino acids determined so far include Arg, Asp, Cys, Glu, Met, Trp, and Asn-Gly. The procedure is demonstrated on beta-galactosidase and lambda immunity 434 repressor protein. One of the uses of the procedure, the identification and localization of point mutations within the sequence, is illustrated using lambda immunity 434 repressor protein.