FIG. 1.

Tax binds to both the CR2 and C/H1-KIX domains of CBP. (A) Schematic representation of the 2,441-aa cellular coactivator CBP. The regions tested for Tax binding are indicated. HAT, histone acetyltransferase domain. (B) Tax binds to the CR2 domain in vitro. Purified recombinant Tax (50 pmol) was incubated with GST alone or the indicated GST-CBP fusion protein (50 pmol each). As controls, Tax binding to GST-C/H1_aa302–409 and GST-C/H1-KIX_aa302–683 was also assayed. The bound proteins were separated by SDS–12% PAGE, transferred to nitrocellulose, and detected using an anti-His₆ antibody. The positions of bound Tax and protein molecular size standards are indicated (in kilodaltons). (C) Coomassie-stained SDS–12% PAGE showing the GST fusion proteins used in panel B. Asterisks denote GST fusion proteins, and protein molecular size standards are indicated in kilodaltons. (D) Tax binds to the CR2 domain in vivo. Growth phenotypes of the designated DNA-binding (DB) and activation domain (AD) constructs were assayed by streaking cells on plates lacking histidine and containing 10 or 20 mM aminotriazole (AT). Plates were analyzed following 5 days of incubation at 30°C.