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采用异硫氰酸胍－酚－氯仿抽提法从孵育至１２ｄ的鸡胚视叶顶盖中提取ＲＮＡ。根据Ｓｃｈｏｅｐｆｅｒ报道的序列设计引物，引物的５′端添加ＥｃｏＲⅠ和ＸｂａⅠ酶切位点。通过逆转录聚合酶链反应（ＲＴ－ＰＣＲ）得到１．４８ｋｂ长的ｃＤＮＡ片段，用ＥｃｏＲⅠ和ＸｂａⅠ酶切ｃＤＮＡ后插入质粒ｐＵＣ１９。测序采用Ｓａｎｇｅｒ双脱氧终止法，结果与文献报道一致。将β２基因克隆入ｐＢＶ２２０原核表达载体中。宿主菌经４２℃诱导，经ＳＤＳ－ＰＡＧＥ蛋白电泳，在相对分子质量（Ｍｒ）５．４×１０４处较对照多一条带
RNA was extracted from the capsid of chicken embryo incubated to 12 days by guanidinium isothiocyanate - phenol - chloroform extraction. Primers were designed according to the sequence reported by Schoepfer. EcoR I and Xba I restriction sites were added to the 5 ’end of the primer. A 1.48 kb cDNA fragment was obtained by reverse transcription polymerase chain reaction (RT-PCR), and the plasmid pUC19 was inserted after digesting cDNA with EcoRI and XbaI. Sequencing using Sanger dideoxy termination method, the results reported in the literature. The β2 gene was cloned into pBV220 prokaryotic expression vector. The host strain was induced at 42 ℃ and electrophoresed by SDS-PAGE. At a relative molecular weight of 5.4 × 104 (Mr), one more band