FIG 4.

LXCXE binding cleft in the RB1 protein is not necessary for MmuPV1 E7 binding. SAOS-2 human osteosarcoma cells were transfected with expression vectors for wild-type RB1 or the RB1^L mutant that contains three amino acid mutations in the LXCXE binding cleft in combination with MmuPV1 or HPV16 E7 expression vectors. MmuPV1 E7 binds wild type and RB1^L with similar efficiency, whereas HPV16 E7 binds and causes degradation of RB1 but not RB1^L. The results shown are representative of two independent experiments. A cartoon of the RB1^L mutant is shown at the top.