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Published June 23, 1998 | Published
Journal Article Open

Human CUL1 forms an evolutionarily conserved ubiquitin ligase complex (SCF) with SKP1 and an F-box protein


The SCF ubiquitin ligase complex of budding yeast triggers DNA replication by catalyzing ubiquitination of the S phase cyclin-dependent kinase inhibitor SIC1. SCF is composed of three proteins-ySKP1, CDC53 (Cullin), and the F-box protein CDC4-that are conserved from yeast to humans. As part of an effort to identify components and substrates of a putative human SCF complex, we isolated hSKP1 in a two-hybrid screen with hCUL1, the closest human homologue of CDC53. Here, we show that hCUL1 associates with hSKP1 in vivo and directly interacts with both hSKP1 and the human F-bos protein SKP2 in vitro, forming an SCF-like particle. Moreover, hCUL1 complements the growth defect of yeast cdc53(ts) mutants, associates with ubiquitination-promoting activity in human cell extracts, and can assemble into functional, chimeric ubiquitin ligase complexes with yeast SCF components. Taken together, these data suggest that hCUL1 functions as part of an SCF ubiquitin ligase complex in human cells. Further application of biochemical assays similar to those described here can now be used to identify regulators/components of hCUL1-based SCF complexes, to determine whether the hCUL2-hCUL5 proteins also are components of ubiquitin ligase complexes in human cells, and to screen for chemical compounds that modulate the activities of the hSKP1 and hCUL1 proteins.

Additional Information

© 1998 by the National Academy of Sciences. Edited by Alexander Varshavsky, California Institute of Technology, Pasadena, CA, and approved April 17, 1998 (received for review February 24, 1998). This paper was submitted directly (Track II) to the Proceedings office. We thank R. Brent, M. Goebl, D. Morgan, H. Zhang, P. Sorger, W. Harper, P. Jackson, S. Handeli, and R. Cohen for generously providing strains, libraries, clones, antibodies, recombinant baculoviruses, and other reagents. We also thank W. Dunphy, R. Feldman, J. Kroll, and R. Verma for critically reading the manuscript and members of the laboratory for helpful discussions. R.J.D. was supported by a grant from the National Institutes of Health (GM52466–01) and by Scholar Awards from Searley Chicago Community Trust and the Burroughs-Wellcome Foundation. C.C.C. is a recipient of a Postdoctoral Fellowship Award from the Leukemia Society of America (Ref. # 5172–97). The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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