A 37-year-old HIV-positive man presents for evaluation of anogenital lesions. He states that the lesions have been present for years, but have recently grown in size and become pruritic and tender. On examination he is circumcised and has multiple hyperkeratotic papules on his penis shaft, perineum, and anal area. He also has a palpable rectal mass with guaiacpositive stool and conjunctival pallor. On further questioning, he admits to recent unintentional weight loss, constipation, and bloating. His CD4+ cell count is 150/mm3 and his hematocrit is 26%. CT of the abdomen shows a 3 x 4-cm rectal mass with multiple metastatic lesions in his liver. What tumor-suppressor protein is targeted by the virus causing this patient’s rectal cancer?