FIG. 4.

Binding of HBV RT to ɛ mutants. (A) HTPRT/Drd was incubated with ³²P-labeled wild-type HBV ɛ RNA, as described for Fig. 2, in the presence of the indicated unlabeled RNA competitors (Compet). The RNA mutants are schematized in the secondary-structure model. Deletions are denoted by dotted lines and substitutions by thick lines. Refer to Fig. 7 for the exact deletions/substitutions in each of the ɛ mutants tested. HE is a 190-nt-long HBV RNA, encompassing DR1 5′ of ɛ, ɛ, and 80 nt 3′ of ɛ (see Materials and Methods for details). The DHBV ɛ and tRNA, which cannot bind to the HBV RT (21), were used as nonspecific competitors. All competitor RNAs were used at a 100-fold molar excess. Note that all reactions also contained an additional 300-fold molar excess of tRNA over the labeled probe (21). (B) HTPRT/Drd (lanes 1 to 7) or HTPRT/Spe (lanes 8 to 11) was tested for binding to the ³²P-labeled HBV ɛ RNA mutants, as described for Fig. 2.