RNA synthesis by RNA polymerase was established in vitro by several laboratories by 1965; however, the RNA synthesized by these enzymes had properties that suggested the existence of an additional factor needed to terminate transcription correctly.
由RNA聚合酶合成RNA是由几个实验室在1965年以前在体外(In vitro)建立的; 然而，由这些酶合成的RNA具有表明存在正确终止转录所需的额外因子的特性。