A missense mutation (Asn to Lys) generated at codon 108 (N108K) via site directed mutagenesis was incorporated, along with an intronic floxed neo cassette, at the endogenous locus by homologous recombination. This mutation recapitulates the mutation responsible for Presbyterian hemoglobinopathy. The amino acid substitution was confirmed by RP-HPLC and mass-spectrometric analysis of purified beta chain.