FIG. 4.

Extension from PPT62 at a nick or a gap followed by M-MuLV RNA. (A) Schematic of model substrates. (B, C, and D) 5′ end-labeled PPT62 was annealed with downstream oligonucleotide MLVnick to template 2 to create a nick, with downstream oligonucleotide MLV2b to template 2A to create a gap of 2 bases, with downstream oligonucleotide MLV5b to template 2B to create a gap of 5 bases, or with downstream oligonucleotide MLV12b to template 2C to create a gap of 12 bases following the 3′ end of PPT62, as indicated. Control extensions were carried out with 5′ end-labeled PPT62 without downstream oligonucleotide on each template strand (none), and all samples were analyzed as described in the legend to Fig. 2. Extensions were done with T7 DNA polymerase (T7; panel B, lanes 1 to 8) or T4 DNA polymerase (T4; panel B, lanes 9 to 16) for 15 min or with H⁻ RT (C), or RTΔH (D) for the indicated times. The positions of unextended PPT62 are indicated on the right.