RNA polymerase – The third class of primases

Abstract.

Multisubunit RNA polymerase transcribes DNA in all living organisms. RNA polymerase is also known to synthesize DNA replication primers in some replication systems, a function that is commonly performed by primases. There are two unrelated types of primases, the bacterial and eukaryal-archaeal types; RNA polymerase has no evolutionary relationship to either type. Here we discuss the mechanism of primer synthesis by RNA polymerase and compare it to mechanisms used by primases of both types as well as to the mechanisms used by RNA polymerase during transcription.