Transcription repressor involved in regulation of protection against UV. Mediates transcriptional repression of CYP73A5, the gene encoding trans-cinnamate 4-monooxygenase, thereby regulating the accumulation of the UV-protectant compound sinapoylmalate. Interacts with BHLH12/MYC1 and BHLH42/TT8 (PubMed:15361138). Interacts with SAD2 (PubMed:17993626). Widely expressed at low level. Highly expressed in siliques. Weakly expressed in seedlings, young and mature leaves, cauline leaves, stems, flower buds and roots. Down-regulated by exposure to UV-B light. Defects lead to a better tolerance of UV-B irradiation due to the increase in sinapate ester accumulation.