 The cell cycle has four stages (G1, S, G2 and M) and Tax is known to accelerate the transition between G1 and S phase.Two DNA repair pathways (base excision repair and nucleotide excision repair) are affected by Tax, leading to mutations in DNA; a classical hallmark of cancer.Tax also causes aneuploidy (abnormal chromosome numbers), which is a possible cause of transformation (normal cells becoming cancer cells).