猬迭宫绦虫幼虫一个含重复序列的cDNA的分子克隆

MOLECULAR CLONING OF A cDNA ENCODING AN ANTIGENIC POLYPEPTIDE CONTAINING REPEAT UNITS OF SPIROMETRA ERINACEIEUROPAEI PLEROCERCOID*

目的：研究猬迭宫绦虫幼虫－裂头蚴的某些蛋白抗原的基因结构。方法：用鼠抗猬迭宫绦虫裂头蚴多克隆抗体筛选裂头蚴ｃＤＮＡ文库，筛选出的阳性克隆经亚克隆，测序后，用微机分析其一级结构。并用Ｎｏｒｔｈｅｒｎ杂交实验检测与ｃＤＮＡ杂交的ｍＲＮＡ长度。结果：从ｃＤＮＡ文库中筛选出一个长度为１０８４ｂｐ的克隆，此克隆的开放读码框为８２８ｂｐ，编码２７６个氨基酸。开放读码框内有一个由１２３个核苷酸组成的重复单位，此重复单位在开放读码框内重复５次。重复单位编码的４１个氨基酸内疏水性氨基酸占５３．７％。Ｎｏｒｔｈｅｒｎ杂交结果显示在１．１ｋｂ处有一个很强的杂交带，１．７ｋｂ处有一个弱的杂交带。１．１ｋｂ处的杂交带与ｃＤＮＡ克隆的长度几乎相等。结论：裂头蚴在宿主体内移行或停留时，这些含重复序列的抗原性多肽可能作为逃避抗原，使裂头蚴在体内逃避免疫系统的杀伤作用。

AIM:To study the gene structure encoding some antigenic polypeptides of plerocercoid of Spirometra erinaceieuropaei (SEP). METHODS:A cDNA library constructed from SEP was immunoscreened using mouse anti SEP polyclonal antibody.The gene structure was analyzed by computer after the insert of positive clone was subcloned and the nucleotide sequences of the insert were determined.The length of mRNA hybridized with cDNA was detected by Northern blotting. RESULTS:A cDNA clone of 1 084 bp encoding an antigenic polypeptide was isolated. The clone contained one open reading frame composed of 828 bp encoding 276 amino acids.The open reading frame contained tandem repeating unit of 123 bp which appeared 5 times in this clone.The 41 amino acids deduced from 123 bp repeating unit consisted of 53 7% of hydrophobic amino acid residues.In Northern blot assay of poly (A) +RNA,a strong band of about 1 1 kb and a weak band of about 1 7 kb were found in the plerocercoids but no band was found in the adult worms. CONCLUSION:The repeating element derived from the plerocercoids may be associated with the migration of the plerocercoids in the host tissue.The polypeptides with repeating element may act as evasive antigens of the parasite to escape from the destruction of host immune reactions.