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Example sentences for: atcop
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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.
Comparison of the subcellular localization signals uncovers clear distinctions between AtCOP1 and MmCOP1.
This speculation would be consistent with the fact that the subcellular localization of AtCOP1 is regulated by light only in certain types of plant cells [ 14 ] . Furthermore, the protein fragments responsible for regulating subcellular localization of AtCOP1 are quite conserved in MmCOP1, which may explain why the mammalian COP1, when expressed in onion epidermal cells, can be regulated by light in a similar manner as AtCOP1 [ 20 ] . However, the same nuclear translocation signal of AtCOP1 has been used in all plant cell types examined [ 17 19 ] , which argue against the later hypothesis.
In contrast, the AtCOP1 NLS has been identified as a classic bipartite nuclear localization signal, consisting of 21 amino acids in the intermediate region of coiled-coil domain and the WD-40 domain [ [ 17 ] ; Fig 8].
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