CDNA CLONING AND CHARACTERIZATION OF RAT SALIVARY GLYCOPROTEINS - NOVEL MEMBERS OF THE PROLINE-RICH-PROTEIN MULTIGENE FAMILIES

The cDNAs for two glycoproteins, the 158-kDa submandibular glycoprotei n (SGP158) and the 200-kDa parotid glycoprotein (PGP200), have been cl oned from rat submandibular and parotid glands, respectively. Both cDN As encode for identical proteins with repeating peptides ln-Gly-(Asn)- Gln-Thr-Gln-Pro-Arg-Pro-Pro-His-Pro-. A full-length cDNA encoding SGP1 58 was obtained using the strategy of anchor-PCR, and a full-length cD NA of PGP200 was prepared using RNA-PCR. Sequence analysis of the cDNA s revealed that SGP158 and PGP200 are identical proteins with 23 repea ting peptides. Twenty-one peptides contain potential N-glycosylation s ites and these two glycoproteins differ only in their glycosylation pa tterns. Southern-blot analysis showed that a single-copy gene encodes both mRNAs. PGP200 is constitutively expressed, but the synthesis of S GP158 is totally dependent upon treatment of animals with the beta-ago nist isoproterenol. The first 106-nucleotide sequence of cDNAs for PGP 200 and SGP158, which corresponds to the 5'-untranslated region and se quence encoding the signal peptide, is highly conserved when compared with proline-rich protein and glutamine-rich protein gene sequences. B ased on the nucleotide sequences of exon I, a phylogenetic tree was co nstructed for 35 members of these multigene families. The tree fits wi th the generally recognized phylogeny of mammalian orders. We propose that exon I sequences of the proline-rich protein and glutamine-rich p rotein multigene families are relatively new and are possibly generate d through exon shuffling during evolution.