Figure 1.

Schematic of a SMRTbell™ template. (A) A SMRTbell template consists of a double-stranded region (the insert) flanked by two hairpin loops. The hairpin loops present a single-stranded region to which a sequencing primer can bind (orange). (B) As a strand-displacing polymerase (gray) extends a primer from one of the hairpin loops, it uses one strand as the template strand and displaces the other. When the polymerase returns to the 5′-end of the primer, it begins strand displacement of the primer and continues to synthesize DNA (moving in the direction of the blue arrow). Therefore, the length of sequence obtained from these templates is not limited by the insert length. Furthermore, the resulting sequence is derived from both sense- and anti-sense strands.