HY5 is required for UV-B-activated gene expression, and its transcriptional activation is independent of phytochromes A and B. RNA gel blot analysis of 10 μg of RNA isolated from UV-treated (under cutoffs WG327, WG305, and WG295, or unfiltered under quartz glass) and nontreated (C) 7-day-old seedlings (wild-type Ler and Col, mutants cry1cry2, hy5, phyAphyB, and uvr2). Blots were sequentially hybridized with specific probes for the indicated genes. Ethidium-bromide-stained rRNA is shown as loading control. Note that a HY5-related transcript is detectable in the hy5-1 mutant. Our RT-PCR amplification and its sequencing confirmed the transcription of the HY5-1-mutant allele (data not shown), which has the fourth codon (CAA = Q) substituted for a stop codon (=TAA) (as published in ref. 34), preventing HY5 protein synthesis in the hy5-1 mutant (4).