Construction and structure of chimeric endonucleases. (a) A schematic representation of fusion proteins constructed into pET21b for expression in Escherichia. coli is shown with the restriction sites. EN, TRAS1 endonuclease domain; FN, restriction endonuclease Fok I cleavage domain; TRF1, human telomere binding protein; TRFH, TRF heterodimerization region; NLS, nuclear localization signal; Myb, telomeric DNA binding motif. Estimated molecular weight and linker length are shown. (b) A model of the chimeric protein M-EN is shown with the N-terminal TRF1 Myb domain in green, the C-terminal TRAS1EN in cyan, and the interdomain hypothetical linker in yellow.