Nanopore DNA sequencing is a single molecule sequencing method in which DNA is pulled through a nanometer-sized pore, while the nucleotides modulate an ionic current. We use a protein pore based on Mycobacterium smegmatis porin A (MspA) that we developed to have sensitivity to single nucleotides in DNA. When using the phi29 DNA polymerase to move DNA in single-nucleotide steps through MspA, we observe a succession of well resolved ionic current levels. Each current level is primarily determined by the two nucleotides centered in MspA's narrowest constriction and is partially influenced by the flanking nucleotides. We present progress towards decoding algorithms that translate the observed ionic current patterns to DNA sequence.