贾第虫表面变异抗原基因的克隆与序列测定

目的 :对比分析编码 90 k Da的表面变异蛋白 ( VSP)基因与已发表的其它 VSP基因。方法 :应用聚合酶链反应 ( PCR)技术、PCR产物的克隆技术和插入基因片段的序列测定。结果 :从贾第虫 0 2 - 4 A1基因组中将编码 90 k Da的表面变异蛋白几乎全长的基因调出 ,经序列分析 ,此基因长度为 2 0 19bp,编码 654个氨基酸 ,具有一个开放阅读框架。推导出的氨基酸序列的半脱氨酸含量丰富 ( 11.8mol% ) ,而且多数的半脱氨酸以 CXXC基序重复出现 2 6次。苏氨酸含量为 11.3mol% ,甘氨酸为 10 .9mol% ,丙氨酸为 10 .1mol%。序列分析发现有 2个天冬酰氨连接的糖基位点。结论 :象其他 VSPs一样 ,CRISP90具有一个高度保守疏水性 C末端。经同源性比较发现 ,与 CRP72有 56%的同源性。这一结果对研究贾第虫株的表面变异抗原基因的表达具有一定的意义。

CLONING AND SEQUENCING OF A VARIANT-SPECIFIC SURFACE ANTIGEN GENE OF GIARDIA LAMBLIA

AIM:To analyse the gene encoding a 90 k Da variant- specific- surface protein ( CRISP90 ) expressed by a Giardia isolate,0 2 - 4 A1in comparison to the variant- specific- surface protein( VSP) gene.METHODS:The polymerase chain reaction( PCR) ,the cloning PCR product and the sequencing of the inserted gene fragment were used.RESUL TS:The near- full length CRISP90 gene was found to be 2 0 19bp long,encode a 654amino acid polypeptide and contained a single open reading frame ( ORF) .The deduced polypeptide sequence is rich in cysteine ( 11.8 mol% ) ,most of which occur within2 6copies of the4 - amino acid CXXC motif.This polypeptide is also rich in threonine( 11.3mol% ) ,glycine( 10 .9mol% ) and alanine( 10 .1mol% ) and in- cludes two NXS consensus N- linked glycosylation sites.CONCL USION:L ike other previously i- dentified VSPs,it contains a highy conserved hydrophobic C- terminal region.The gene sequence showed56% homology with the CRP72 .