Figure 1: 454 sequencing. (a) Genomic DNA is isolated, fragmented, ligated to adapters and denatured into single strands. (b) DNA fragments are bound to Streptavidin coated magnetic beads under conditions that allow one fragment per bead, the beads are isolated and grouped in the droplets of a PCR-reactionmixture- in-oil emulsion and PCR amplification occurs within each droplet. (c) The emulsion is broken, the DNA strands are denatured, and beads carrying single-stranded DNA templates are enriched (not shown) and deposited into wells of a fiber-optic slide. (d) Smaller beads carrying enzymes required for a solid phase pyrophosphate sequencing reaction are deposited into each well. (e) Scanning electron micrograph of a portion of a fiber-optic slide, showing fiber-optic cladding and wells before bead deposition. (f) The 454 sequencing instrument consists of the following major subsystems: a fluidic assembly (object i), a flow cell that includes the well-containing fiber-optic slide (object ii), a CCD camerabased imaging assembly with its own fiber-optic bundle used to image the fiber-optic slide (part of object iii), and a computer that provides the necessary user interface and instrument control (part of object iii) (Figure reproduced from Rothberg et al with permission from [10]).