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新型蛋白质的分子克隆基本依靠ｃＤＮＡ文库的筛选，而文库构建的载体多为λｇｔｌｌ。由于λｇｔｌｌＤＮＡ分子量较大（４９ｋｂ），提取过程中多用ＰＥＧ，因此λｇｔｌｌｃＤＮＡ克隆及其直接序列测定极为困难。为克服此困难，作者自行设计了不含克隆位点的一对公用λｇｔｌｌＰＣＲ引物。试用表明，此引物通过改变ＰＣＲ反应条件，可特异性地扩增多种彼此独立的ｃＤＮＡ。经亚克隆后的序列测定表明，用此方法扩增克隆的多种ｃＤＮＡ保留了原有阅读框架和ｐｏｌｙＡ特有序列，因而基本解决了新型蛋白质分子克隆中ｃＤＮＡ亚克隆与序列测定的困难．
The molecular cloning of novel proteins relies mainly on the screening of cDNA libraries, while the library-building vectors are mostly λgtll. Because λgtllDNA has a large molecular weight (49kb) and PEG is used in the extraction process, the λgtll cDNA cloning and its direct sequence determination are extremely difficult. To overcome this difficulty, the authors designed a pair of common λgtllPCR primers containing no cloning site. Experiments showed that this primer could specifically amplify a variety of independent cDNAs by changing the conditions of the PCR reaction. The subcloning sequence analysis showed that this method to expand the cloned cDNA retains the original reading frame and polyA unique sequences, thus basically resolving the new protein molecular cloning cDNA subcloning and sequence determination difficulties.