PRB1 gene variants coding for length and null polymorphisms among human salivary Ps, PmF, PmS, and Pe proline-rich proteins (PRPs)

• Published in: American journal of human genetics 1993-01, Vol.53 (1), p.264-278
• Main Authors: Azen, E A, Latreille, P, Niece, R L
• Format: Article
• Language: English
• Subjects: alleles; amino acid sequence; genes; man; nucleotide sequence; point mutation; PRB1 gene; predictions; proline-rich proteins
• ISSN: 0002-9297

Six closely linked PRP (proline-rich protein) genes code for salivary PRPs that show frequent length and null polymorphisms. We report assignment of Ps proteins to the PRB1 gene, the derived primary structures of Ps 1 and Ps 2 proteins, and the molecular basis for some null alleles among PRB1-coded PRPs (Ps, PmF, PmS, and Pe). The derived primary structures of Ps 1 and Ps 2 proteins were determined by sequencing exon 3 of the different-length PRB1M (medium) and PRB1L (large) copies from subject C.J. with the Ps 1-2 phenotype. The PRB1L copy (coding for Ps 2) contained three additional tandem repeats within the Ps coding region, and the different-length Ps 1 and Ps 2 proteins can be explained on this basis. The molecular basis for the Ps 0 and the Pe- phenotypes was determined in another individual (M.V.O., a PRB2/1 fusion-gene heterozygote) with a single PRB1L copy. A premature stop mutation (CGA (Arg) arrow right TGA (stop)) occurred at residue 61 in the Ps-coding region. The identical mutation was found in the PRB1L and PRB1/2S (small) copies of a second individual (E.A.) with reduced Pe protein and the Ps O phenotype. This individual is a PRB1/2 fusion-gene heterozygote (Azen et al. 1992) with probably three mutated PRB1 copies (PRB1L-PRB1L-PRB1/2S). DNA sequences of the postulated crossover region of the PRB1/2S fusion-gene copy supported the postulated crossover. The PmF- and PmS- phenotypes in the three subjects were due to both the stop mutation and the lack of suitable proteolytic cleavage sites in the PRB1-coded precursor proteins.