Chemical synthesis and cloning of a poly(arginine)-coding gene fragment designed to aid polypeptide purification

A 43-bp DNA duplex coding for poly(arginine) [poly(arg)] has been synthesised by modified phosphotriester procedures. It has been inserted into the Bg/II and BamHI restriction sites of a cloned synthetic beta-urogastrone (Uro) gene, under the control of the trp promoter. Subsequent induction with 3 beta-indole acrylic acid produces beta-Uro with a C-terminal poly(arg) fusion. The raised isoelectric point of this polypeptide fusion facilitates rapid purification by cation exchange chromatography. The C-terminal poly(arg) tail can be readily removed by treatment with carboxypeptidase B.