RB1 and papilloma: Papillomas caused by the MmuPV1 E7D90A quasivirus were significantly smaller than those caused by MmuPV1 (MmuPV1 versus MmuPV1 E7D90A, P = 0.003, two-sided t test), indicating that the loss of E7’s ability to interact with Rb1 correlates with reduced size of MmuPV1-induced papillomas.