Evolution of TALENs
Engineered transcriptional activator-like effectors (TALEs) are versatile tools for genome manipulation with applications in research and clinical contexts. One current drawback of TALEs is that the 5′ nucleotide of the target is specific for thymine (T). TALE domains with alternative 5′ nucleotide specificities could expand the scope of DNA target sequences that can be bound by TALEs. This disclosure provides methods and strategies for the continuous evolution of proteins comprising DNA-binding domains, e.g., TALE domains. In some aspects, this disclosure provides methods and strategies for evolving such proteins under positive selection for a desired DNA-binding activity and/or under negative selection against one or more undesired (e.g., off-target) DNA-binding activities. Some aspects of this disclosure provide engineered TALE domains and TALEs comprising such engineered domains, e.g., TALE nucleases (TALENs), TALE transcriptional activators, TALE transcriptional repressors, and TALE epigenetic modification enzymes, with altered 5′ nucleotide specificities of target sequences. Engineered TALEs that target ATM with greater specificity are also provided.
1. A protein comprising a TALE N-terminal domain having an amino acid sequence that is at least 95% identical to the amino acid sequence provided in SEQ ID NO: 1, wherein the amino acid sequence comprises an alanine to glutamic acid amino acid substitution at the amino acid residue corresponding to position A39 of SEQ ID NO: 1 and/or a lysine to glutamic acid substitution at the amino acid residue corresponding to position K19 of SEQ ID NO:1, wherein the protein has DNA-binding activity.
2. The protein of claim 1 , wherein the amino acid sequence is at least 98% identical to the amino acid sequence provided in SEQ ID NO: 1.
3. The protein of claim 1 , wherein the amino acid sequence further comprises an alanine to glutamic acid substitution at the amino acid residue corresponding to position A93 of SEQ ID NO: 1.
4. The protein of claim 1 , wherein the amino acid sequence further comprises a glycine to arginine amino acid substitution at the amino acid residue corresponding to position G98 of SEQ ID NO: 1.
5. The protein of claim 1 , wherein the amino acid sequence further comprises one or more amino acid substitutions at the positions corresponding to S22, G77, A85, T91, A93, P99, A139, and N136 of SEQ ID NO: 1.
6. The protein of claim 1 , wherein the amino acid sequence further comprises an arginine to tryptophan amino acid substitution at the amino acid residue corresponding to position R21 of SEQ ID NO: 1.
7. The protein of claim 1 , wherein the protein comprises a TALE repeat array that binds a target sequence comprised in a genome.