The presence of multiple rat DSP-PP transcripts

Phosphoproteins or phosphophoryns (PPs) are the most abundant (> 50%) non-c ollagenous proteins (NCPs) in dentin. PPs bind to calcium and hydroxyapatit e and are believed to play a crucial role in dentin mineralization. Dentin sialoprotein (DSP), a highly glycosylated protein, comprised 5-8% of NCPs i n dentin. The coding sequences for these two major NCPs are known to be con tiguously located (i.e. DSP-PP) at the cDNA and genomic DNA levels in both rat and mouse. Previous studies have demonstrated the presence of multiple DSP-PP transcripts in the total RNA of adult rat incisors. To further under stand the nature of these multiple transcripts, we performed reverse transc ription-PCR and obtained a PP cDNA variant which encoded a 171 amino acid p eptide (PP171) that shares many of the same characteristics as that of the published rat PP240 sequence [Ritchie, H.H. and Wang, L.-H., J. Biol. Chem. 271 (1996) 21695-21698]. Due to its reduced size, as compared to PP240, th is cDNA encodes a phosphorylated protein with a reduced negative charge tha t may differentially affect mineralization processes. We provide evidence t hat there are multiple DSP-PP transcripts with various sizes of PP sequence s in rat. (C) 2000 Published by Elsevier Science B.V.