Nat. Biotechnol. 21, 191–194 (2003)

On page 191, information about a mutant was omitted. The last sentence of the third paragraph should read as follows:

Among the mutant proteins screened, the asCP A148G mutant with random substitutions F7L, Y26C, T30I, A142V (designated KFP1, GenBank accession no. AY233273) demonstrated the most remarkable properties, which make it suitable as a photoactivated fluorescent label.

On page 192, last full paragraph, the irradiation time for the irreversible KFP1 activation in mitochondria was listed incorrect. The sentence should read:

Brief irradiation (fast mode, 20 seconds) with 30% power green laser light induced irreversible kindling of KFP1 in mitochondria within the irradiated field.