CCCTC-binding factor variants

1. An engineered CCCTC-binding factor (CTCF) variant comprising at least one amino acid residue in at least one zinc finger that differs in sequence from the amino acid sequence of a wild-type CTCF, wherein the engineered CTCF variant binds to a mutant CTCF binding sequence (CBS) with a higher affinity than wild-type CTCF,

wherein the mutant CBS has G, G, and A residues at positions 2, 5, and 11 of the consensus CBS motif, respectively, and the engineered CTCF comprises:

(i) the amino acid sequence GNLVR (SEQ ID NO: 117), GNLRR (SEQ ID NO: 118), GNLAR (SEQ ID NO: 138), GNLMR (SEQ ID NO: 139), ANLRR (SEQ ID NO: 69), SNLRR (SEQ ID NO: 116), or NNLRR (SEQ ID NO: 121) at ZF4 positions +2 to +6 of the engineered CTCF;

(ii) the amino acid sequence EHMNR (SEQ ID NO: 126), EHMKR (SEQ ID NO: 123), EHMRR (SEQ ID NO: 34), SHMNR (SEQ ID NO: 146), SHMRR (SEQ ID NO: 147), THMKR (SEQ ID NO: 33), or DHMNR (SEQ ID NO: 32) at ZF6 positions +2 to +6 of the engineered CTCF; and

(iii) the amino acid sequence EHLKV (SEQ ID NO: 13), EHLAE (SEQ ID NO: 151), STLNE (SEQ ID NO: 152), DHLQV (SEQ ID NO: 12), EHLNV (SEQ ID NO: 9), DHLNT (SEQ ID NO: 155), EHLQA (SEQ ID NO: 156), or HHLMH (SEQ ID NO: 157) at ZF7 positions +2 to +6 of the engineered CTCF.

2. A pharmaceutical composition comprising an engineered CTCF variant according to claim 1 .

3. A gene expression system for regulation of a gene, the system comprising a nucleic acid encoding an engineered CTCF variant according to claim 1 .

4. A kit comprising an engineered CTCF variant according to claim 1 .

5. A nucleic acid encoding an engineered CTCF variant according to claim 1 .

6. A method of altering expression of a gene under the control of a mutant CBS, wherein the mutant CBS has G, G, and A residues at positions 2, 5, and 11 of the consensus CBS motif, respectively, the method comprising contacting the mutant CBS with an engineered CTCF according to claim 1 , thereby regulating the expression of the gene.