Words similar to hy
Example sentences for: hy
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Instead, CIP8, an AtCOP1 interacting RING-H2 finger protein, is found to ubiquitinate HY5 in vitro [ 50 51 ] . Therefore, it is possible that COP1 may recruit other RING finger proteins, such as CIP8, to mediate the ubiquitination of specific substrates.
AtCOP1 contains three conserved structural domains: a RING finger at the amino terminus, a coiled-coil domain in the middle, and a carboxyl-terminal WD40 repeat domain [ 9 10 ] . Each of the three conserved domains has been shown to mediate protein-protein interactions [ 11 12 13 ] . The subcellular localization of AtCOP1 is regulated by light in a tissue specific manner [ 14 15 ] . The hypocotyl cell nuclei contain high levels of COP1 in the dark and reduced levels in the light, suggesting that the nucleocytoplasmic partitioning of AtCOP1 is adjusted by a light-responsive mechanism [ 14 16 ] . The activity of AtCOP1 is at least in part regulated by its subcellular localization, as the degradation of HY5 is dependent upon the nuclear accumulation of AtCOP1 in the dark [ 4 ] . AtCOP1 was demonstrated to carry a single, bipartite nuclear localization signal located between the coiled-coil domain and the WD-40 domain (amino acid 294-314) and a cytoplasmic localization signal, which was mapped to a region partially overlapping with the RING finger and the coiled-coil domain (amino acid 67-117) [ 17 ] . Strikingly, AtCOP1 protein forms characteristic nuclear speckles when transiently expressed in onion epidermal cells or stably expressed in transgenic Arabidopsis [ 6 18 ] . The functional role of these speckles is currently unknown; however, a subnuclear localization signal consisting of 58 residues (amino acid 120-177) is required for their formation [ 19 ] .
COP10, which has been shown to interact with AtCOP1 in yeast two-hybrid experiment, encodes a ubiquitin conjugating enzyme (E2) variant [ 44 ] . The COP9 signalosome, an eight-subunit complex homologous to the lid subcomplex of the 26 S proteasome [ 45 ] , directly associates with SCF E3 complex and promotes deneddylation of the cullin subunit of SCF in both plant and animal cells [ 46 47 48 49 ] . The exact relationship between COP1 and the COP9 signalosome remains obscure; it is known, however, that in Arabidopsis the COP9 signalosome is required for COP1 to accumulate in the nucleus in the dark [ 29 ] . Although COP1 most likely plays a role in regulating protein degradation, attempts in reconstituting ubiquitination of HY5 by AtCOP1 have been unsuccessful.
Because of its role in mediating the degradation of HY5, HYH, and possibly other transcription factors in Arabidopsis [ 4 5 ] and the presence of a RING finger domain and a WD-40 domain, AtCOP1 has been proposed to function as a RING-finger type ubiquitination E3 ligase, by recruiting E2 through its RING-finger domain and binding to the substrates through the WD-40 repeats [ 4 43 ] . This hypothesis is also supported by the findings about other negative regulators of plant photomorphogenesis.
In A. thaliana , CSN was shown to be required for the efficient nuclear accumulation of the putative RING-type ubiquitin ligase COP1 [ 24], which mediates ubiquitin-dependent degradation of the photomorphogenic transcription factor HY5 [ 25].
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