Molecular genetical and phylogenic studies on human salivary proline-rich protein P-B.

利用聚合酶链式反应技术克隆了人唾液富含脯氨酸蛋白P-B基因。该克隆命名为PBII，并测定了其核苷酸序列(登录号为AB031740)。PbII是AT富含基因，有3个外显子。它与我之前克隆的-pBI有很高的序列同源性。两个基因在整个分子范围内具有同源性。两个基因的外显子2完全相同。每个分子中间部分的同源性较低，PBII的第2内含子长度比PBI长60obp。尽管PBII的外显子3比FBI长，但PBII的基因产物(p-B)比PBI的推测基因产物(P-B1)短55个残基，这主要是由于PBI的终止密码子向3‘方向移动所致。虽然PBII和PBI属于同一个基因家族，但只有PBII基因在人的颌下腺中转录。利用Stan Ford G3辐射杂交作图平台和来自PBII的引物，通过聚合酶链式反应，将PBII基因定位在4号染色体长臂上，靠近Statherin、组蛋白、PBI和泪液中富含Pro的蛋白质，以确定P-B或P-B样蛋白的合成位点。因为牛发育中的釉质中含有类似P-B的蛋白质，所以选择牛作为实验材料。从PCR结果来看，牛的颌下腺、牙胚和牙髓被认为是合成P-B或P-B样蛋白的组织，越来越多的组织被研究将使根据P-B合成组织的共同特征来估计P-B的生理功能成为可能。

The gene encoding human salivary proline-rich protein P-B was cloned by PCR. The clone isolated was named PBII and the nucleotide sequence of PBII was determined (accession number AB031740). PBII is the AT rich gene and has 3 exons. it has high degree of sequence homology with-PBI which I cloned previously. Two genes have homology over the entire range of molecules. Exons 2 of two genes are completely identical. Homology of the middle part of each molecule was relatively low and the length of intron 2 of PBII was longer than that of PBI by 6OObp. In spite that exon 3 of PBII was longer than that of FBI, |the gene product of PBII (p-B) is shorter than the putative gene product (P-Bl) of PBI by 55 residues, mainly because of the shift of stop codon of PBI to 3' direction. Though PBII and PBI belong to the same gene family, only PBII isconsidered to be transcribed in human submaxillary gland.PBII gene was mapped on long arm of chromosome 4 near statherin, histatin, PBI and tear proline rich protein, by PCR using Stan ford G3 radiation hybrid mapping panel and primers derived from PBII.To determine synthesis site of P-B or P-B like protein, mRNAs were prepared from submaxillary gland, tooth germ and tooth pulp of Bos taurus. Bos taurus was chosen as experimental material since bovine developing enamel is known to contain P-B like protein. Judging from PCR results, submaxillary gland, tooth germ and tooth pulp of Bos taurus are considered to be the tissues synthesizing P-B or P-B like protein, increasing numbers of tissues studied will make it possible to estimate the physiological functions of P-B based on the common features of P-B synthesizing-tissues.