DNA-dependent RNA polymerase (RNAP) catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Forms the clamp head domain. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Binds at least 2 Zn(2+) per subunit. (Microbial infection) Interacts with acidianus two-tailed virus protein RIP; this interaction results in the global inhibition of transcription. Part of the 13-subunit RNA polymerase complex. Belongs to the RNA polymerase beta' chain family.