Escherichia coli cells expressing variants of the North American firefly luciferase luminesce in the orange and red regions of the visible spectrum while bacteria synthesizing the wild-type enzyme emit yellow–green light. Single amino acid substitutions isolated by error-prone PCR are responsible for the change in luminescence color. The residues involved are space-filled on a ribbon rendering of Photinus pyralis luciferase. For details, see Shapiro et al., pages 581–587.
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