2 CODING CHANGE MUTATIONS IN THE HIS2(2) ALLELE CHARACTERIZE THE SALIVARY HISTATIN 3-2 PROTEIN VARIANT

The decoded amino acid sequence of a salivary protein variant, histati n 3-2 (formerly termed ph c), that is found primarily and in high freq uency in Black populations was determined by genomic PCR and direct se quencing of the HIS2(2) allele. Two different mutations that cause cod ing changes were found in exon 5. The first mutation is a single nucle otide (T --> A) substitution that causes a TAT (Tyr) --> TAA (Stop) ch ange at residue 28. This premature stop mutation results in a 27 amino acid histatin 3-2 protein, which is 5 amino acids smaller than the co mmon histatin 3-1 allelic protein (a product of the HIS2(1) allele). T he second mutation, a single nucleotide (G --> A) substitution (locate d only 19 nucleotides upstream of the first mutation) causes a CGA (Ar g) --> CAA (Gin) change at residue 22, which eliminates a proteolytic cleavage site. These two mutations explain the differences in electrop horetic patterns of HIS2(1) versus HIS2(2) coded histatin peptides and may have functional significance. Each mutation alters a different DN A restriction site, and this provides a DNA based test for the mutatio ns. This test should greatly simplify population and family studies of this protein polymorphism, since the saliva-based test is considerabl y more problematic, Elucidation here of the derived protein sequence o f the variant histatin 3-2 protein may also facilitate functional stud ies. (C) 1994 Wiley-Liss, Inc.