21. 4 A Zinc finger motif is a DNA-binding domain o呀pQ zn t+ oo②o Figure 21.3 Transcription factor SPl has a series of three zinc fingers, each with a characteristic pattern of cysteine and histidine residues that constitute the zinc-binding site 请莘大Figure 21.3 Transcription factor SP1 has a series of three zinc fingers, each with a characteristic pattern of cysteine and histidine residues that constitute the zinc-binding site. 21.4 A zinc finger motif is a DNA-binding domain