  Nanopore sequencing of DNA is a single-molecule technique that may achieve
long reads, low cost, and high speed with minimal sample preparation and
instrumentation. Here, we build on recent progress with respect to nanopore
resolution and DNA control to interpret the procession of ion current levels
observed during the translocation of DNA through the pore MspA. As
approximately four nucleotides affect the ion current of each level, we
measured the ion current corresponding to all 256 four-nucleotide combinations
(quadromers). This quadromer map is highly predictive of ion current levels of
previously unmeasured sequences derived from the bacteriophage phi X 174
genome. Furthermore, we show nanopore sequencing reads of phi X 174 up to 4,500
bases in length that can be unambiguously aligned to the phi X 174 reference
genome, and demonstrate proof-of-concept utility with respect to hybrid genome
assembly and polymorphism detection. All methods and data are made fully
available.
