FIG. 1.

Mutant X proteins used for identifying regions of HBx required for interaction with XAP-1/UVDDB. (A) The 154-amino-acid HBx protein (black bar). The region known to be important for HBx transactivation of the SV40 early promoter in HepG2 cells (10) is shown as an open box. Open circles above the transactivation domain bar indicate point mutants (codons 58, 64, 74, 82, 107, 111, 114, 126, and 134) whose alteration has no effect on transactivation by HBx in HepG2 cells; an open triangle indicates the point mutation (residue 61) whose alteration reduces or completely abolishes transactivation, depending on the amino acid change; and filled circles below the bar indicate point mutations (codons 69 and 132) whose alteration completely abolishes HBx activity (4, 24, 33). (B) Deletion mutants of HBx. Black bars represent regions of HBx retained in the deletion mutants. Numbers represent amino acids retained in the mutant. XAP-1 binding was measured in the yeast two-hybrid system, with a positive interaction indicated by β-galactosidase activity as described in Materials and Methods. (C) HBx proteins containing point mutations. Mutations were introduced into pAS1-X by site-directed mutagenesis and mutated oligonucleotides. Mutations included a conserved Cys (position 7) changed to Ser; Cys at positions 61 and 69 each converted to Leu; and amino acids at positions 90 and 91 changed to eliminate a Pro and a charged (Lys) residue.