Methods:(CTP)_4coding gene from pBSMR-(CTP)_4 was cloned into prokaryotic expression vector pET-28a(+) and the expression plasmid pET-28a(+)- (CTP)_4was obtained.

• 方法:将pBSMR-(CTP)_4中的(CTP)_4基因片断克隆入表达载体pET-28a(+),得到表达质粒pET-28a(+)-(CTP)_4。