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The structure and evolution of the human salivary proline-rich protein gene family
1Department of Pathology, University of North Carolina, Chapel Hill 27599.
Insights
Researchers sequenced human salivary proline-rich protein (PRP) genes, revealing their evolutionary history. Gene duplications and rearrangements shaped the PRP gene family, influencing protein structure and function.
Area of Science:
- Genomics
- Molecular Evolution
- Human Genetics
Background:
- The human salivary proline-rich protein (PRP) gene family comprises six members.
- PRPs play roles in oral health, including lubrication and protection.
- Understanding PRP gene structure and evolution is crucial for insights into salivary functions.
Purpose of the Study:
- To present the nucleotide sequences of four human salivary PRP genes (PRB1, PRB2, PRB3, PRB4).
- To elucidate the probable evolutionary history of the human PRP gene family.
- To identify structural features contributing to PRP diversity.
Main Methods:
- Nucleotide sequencing of four human PRP genes.
- Comparative sequence analysis of the six PRP genes.
- Phylogenetic analysis to infer evolutionary relationships.
Main Results:
- Detailed nucleotide sequences for PRB1, PRB2, PRB3, and PRB4 were determined.
- Each gene is approximately 4.0 kb with four exons, featuring tandem repeats in exon 3.
- The PRP gene family likely evolved from a single ancestral gene via four duplications, forming three subsets.
- Sequence variations, particularly in tandem repeat numbers, explain allelic length differences.
Conclusions:
- The human PRP gene family evolved through gene duplication and rearrangement events.
- Exon 3, rich in tandem repeats, is a key region for PRP diversity and evolution.
- Understanding PRP gene evolution provides insights into the functional diversification of salivary proteins.
Abstract:
We present the nucleotide sequences of four members of the six-member human salivary proline-rich protein (PRP) gene family. The four genes are PRB1 and PRB2, which encode basic PRPs, and PRB3 and PRB4, which encode glycosylated PRPs. Each PRB gene is approximately 4.0 kb in length and contains four exons, the third of which is entirely composed of 63-bp tandem repeats and encodes the proline-rich portion of the protein products. Exon 3 contains different numbers of tandem repeats in the different PRB genes. Variation in the numbers of these repeats is also responsible for length variations in different alleles of the PRB genes. We have determined a probable evolutionary history of the human PRP gene family by comparing the nucleotide sequences of the six PRP genes. The present-day six PRP loci probably evolved from a single ancestral gene by four sequential gene duplications, leading to six genes that fall into three subsets, each consisting of two genes. During this evolutionary process, multiple rearrangements and gene conversion occurred mainly in the region from the 3' end of IVS2 and the 3' end of exon 3.