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HY4 gene of A. thaliana encodes a protein with characteristics of a blue-light photoreceptor


SPECIFIC responses to blue light are found throughout the biological kingdom. These responses& mdash;which in higher plants include photo-tropism, inhibition of hypocotyl elongation, and stomatal opening1& mdash;are in many cases thought to be mediated by flavin-type photoreceptors2. But no such blue-light photoreceptor has yet been identified or isolated, although blue-light responses in plants were reported by Darwin over a century ago3, long before the discovery of the now relatively well characterized red/far-red light photoreceptor, phytochrome4. Here we describe the isolation of a gene corresponding to the HY4 locus of Arabidopsis thaliana. The hy4 mutant5 is one of several mutants6 that are selectively insensitive to blue light during the blue-light-dependent inhibition of hypocotyl elongation response, which suggests that they lack an essential component of the cryptochrome-associated light-sensing pathway. The HY4 gene, isolated by gene tagging, was shown to encode a protein with significant homology to microbial DNA photolyases. As photolyases are a rare class of flavoprotein that catalyse blue-light-dependent reactions7, the protein encoded by HY4 has a structure consistent with that of a flavin-type blue-light photoreceptor.

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Ahmad, M., Cashmore, A. HY4 gene of A. thaliana encodes a protein with characteristics of a blue-light photoreceptor. Nature 366, 162–166 (1993).

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