15. Which of the following is not true for heterogeneity of the Rpb1 subunit in eukaryotic RNA polymerase II? (A) RNA polymerase II from plasmacytoma showed heterogeneity in its largest subunit. (B) Subunit Ila is un-phosphorylated and is the primary product to join the preinitiation complex of yeast RNA polymerase II. (C) The carboxyl-terminal domain of RNA polymerase II is phosphorylated prior to the formation of the initiation complex. (D) Phosphorylation of Ila is occurred on its carboxyl-terminal domain. (E) RNA polymerase II with IIo is involved in transcription elongation.