Identification and Characterization of human Rsc Chromatin-Remodeling Complex

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The ATP-dependent Chromatin-remodeling complex, Rsc, was originally identified in yeast. It has similar subunit composition as SWI/SNF: 2 subunits are shared between the two complexes and at least 4 others are homologues of each other. However, the function of Rsc is distinct from SWI/SNF. Rsc is essential to the mitotic growth of yeast, whereas SWI/SNF is not. The rsc mutants are arrested at G2/M transition during the cell cycle and this arrest is dependent on the spindle-checkpoint gene. They are also more sensitive to microtubule-destabilizing drugs. These data suggest that Rsc may play a role in mitosis perhaps by stabilizing mitotic spindle formation. We have previously purified several ATP-dependent chromatin remodeling complexes from human which are closely-related to either yeast SWI/SNF or Rsc. By microsequencing and cloning, we now identified one subunit of a particular complex as a human homologue of yeast Rsc subunits, Rsc1 and Rsc2. We subsequently identified many other subunits of human Rsc complex and found many of them to be identical to those in human SWI/SNF. Preliminary data suggest that human Rsc may directly participate in mitosis by binding to microtubules. We are continuing to investigate this part of the mechanism.