Neu1^a

Sequencing of the a allele revealed 5 nucleotide differences compared to the b allele. These changes alter the amino acid residues 11, 15, 17, 19 and 209 of the encoded protein from Gly, Tyr, Ala, Arg and Leu to Arg, Cys, Val, Cys and Ile, respectively. This encoded protein has 85-95% less activity than the protein encoded by the b allele as demonstrated in an in vitro assay. Further studies attributed most of the activity loss to the variation at position 209. Later studies detected 4 silent mutations in the signal peptide sequence and 2 mutations (c.-240C>T and c.-519G>A) in the promoter region. The mutation c.-519G>A creates a novel binding site for Nkx3-1 and Nkx3-2. In vitro assays demonstrated that binding of Nkx3-2 specifically represses promoter driven expression. (J:43930, J:77236, J:147881)