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. 2009 Apr 20;106(19):7702–7707. doi: 10.1073/pnas.0901054106

Fig. 1.

Fig. 1.

Discrimination of immobilized DNA homopolymers by αHL pores. (A) Schematic representation of a homopolymeric DNA oligonucleotide (blue circles, only the first 25 nucleotides of the 60-nucleotide-long sequence are shown) immobilized inside an αHL pore (gray, cross-section) through the use of a biotin (yellow)–streptavidin (red) linkage. The αHL pore can be divided into 2 halves, each ≈5 nm in length; an upper vestibule located between the cis entrance and the central constriction, and a 14-stranded, transmembrane, antiparallel β-barrel, located between the central constriction and trans exit. The central constriction of 1.4 nm diameter is formed by the Glu-111, Lys-147 (shaded green), and Met-113 side chains contributed by all 7 subunits. (B and C Left) Current levels for the WT and E111N/K147N pores when blocked with immobilized poly(dC) and poly(dA) oligonucleotides. (B and C Right) Typical event histograms displaying the residual current levels, caused by poly(dC) and poly(dA) oligonucleotide blockages, for the WT and E111N/K147N pores. The mean residual current levels for each oligonucleotide were determined by performing Gaussian fits to the data.