In prokaryotes, the RNA polymerase holoenzyme consists of ________.
1) the core polymerase plus two alpha subunits.
2) the core polymerase plus two beta subunits.
3) the core polymerase plus two alpha subunits, two beta subunits, and a sigma subunit.
4) the core polymerase plus a sigma subunit.
5) two alpha subunits, two beta subunits, and two sigma subunits.
