text: RNA Pol II elongation promoters can be summarised in three classes:
  # Drug/sequence-dependent arrest affected factors, e.g., SII (TFIIS) and P-TEFb protein families.
  # Chromatin structure oriented factors. Based on histone post translational modifications – phosphorylation, acetylation, methylation and ubiquination.
  #: See: chromatin, histone, and nucleosome
  # RNA Pol II catalysis improving factors. Improve the Vmax or Km of RNA Pol II, so improving the catalytic quality of the polymerase enzyme. E.g. TFIIF, Elongin and ELL families.
  #: See: Enzyme kinetics, Henri–Michaelis–Menten kinetics, Michaelis constant, and Lineweaver–Burk plot
  As for initiation, protein interference, seen as the "drug/sequence-dependent arrest affected factors" and "RNA Pol II catalysis improving factors" provide a very rapid response and is used for fine level individual gene control. Elongation downregulation is also possible, in this case usually by blocking polymerase progress or by deactivating the polymerase.
  Chromatin structure-oriented factors are more complex than for initiation control. Often the chromatin-altering factor becomes bound to the polymerase complex, altering the histones as they are encountered and providing a semi-permanent memory of previous promotion and transcription.