A method of sequencing a target polynucleotide, comprising: (a) contacting the target polynucleotide with a transmembrane pore and a Phi29 DNA polymerase such that the Phi29 DNA polymerase controls the movement of the target polynucleotide through the pore during the target polynucleotide interactions with the pore; and (b) measuring a current passing through the pore during interaction and thereby determining the sequence of the target polynucleotide, wherein steps (a) and (b) are carried out with a voltage applied across the pore while the Phi29 DNA polymerase is bound to the target polynucleotide, and further wherein steps (a) and (b) are carried out: in the absence of free nucleotides and the absence of an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore with the field resulting from the applied voltage, optionally wherein the method further comprises: (c) lowering the voltage applied across the pore such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore; or in the absence of free nucleotides and the presence of an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore with the field resulting from the applied voltage, optionally wherein the method further comprises: (c) adding free nucleotides such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore; or in the presence of free nucleotides and an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore against the field resulting from the applied voltage, optionally wherein the method further comprises: (c) removing the free nucleotides such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore. (a) contacting the target polynucleotide with a transmembrane pore and a Phi29 DNA polymerase such that the Phi29 DNA polymerase controls the movement of the target polynucleotide through the pore during the target polynucleotide interactions with the pore; and (b) measuring a current passing through the pore during interaction and thereby determining the sequence of the target polynucleotide, wherein in the absence of free nucleotides and the absence of an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore with the field resulting from the applied voltage, optionally wherein the method further comprises: (c) lowering the voltage applied across the pore such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore; or in the absence of free nucleotides and the presence of an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore with the field resulting from the applied voltage, optionally wherein the method further comprises: (c) adding free nucleotides such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore; or in the presence of free nucleotides and an enzyme cofactor such that the Phi29 DNA polymerase moves the target polynucleotide through the pore against the field resulting from the applied voltage, optionally wherein the method further comprises: (c) removing the free nucleotides such that the Phi29 DNA polymerase moves the target polynucleotide through the pore in the opposite direction to steps (a) and (b) and nucleotides in the target polynucleotide interact with the pore; and (d) measuring the current passing through the pore during each interaction and thereby proof reading the sequence of the target polynucleotide obtained in step (b), wherein steps (c) and (d) are also carried out with a voltage applied across the pore.