Identification of a Point Mutation in the Human Insulin Gene Giving Rise to a Structurally Abnormal Insulin (Insulin Chicago)

Both insulin gene alleles of a diabetic patient with a mutant insulin were cloned in a lambda vector and their nucleotide sequences were determined. Nucleo-tide sequence analysis revealed, in one allele, a C (cytidylate) to G (guanylate) transversion in the codon for phenylalanine at position 25 of the insulin B-chain. This point mutation leads to the substitution of a leucine for phenylalanine accompanied by the loss of a restriction endonuclease Mboll recognition site and the creation of a new Rsal cleavage site at this position.