Association of yeast SAP1, a novel member of the ‘AAA’ ATPase family of proteins, with the chromatin protein SIN1

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Abstract
The yeast SIN1 protein is a nuclear protein that together with other proteins behaves as a transcriptional repressor of a family of genes. In addition, sin1 mutants are defective in proper mitotic chromosome segregation. In an effort to understand the basis for these phenotypes, we employed the yeast two‐hybrid system to identify proteins that interact with SIN1 in vivo. Here, we demonstrate that SAP1, a novel protein belonging to the ‘AAA’ family of ATPases, is able to directly interact with SIN1. Furthermore, we show, using recombinant molecules in vitro, that a short 27 amino acid sequence near the N‐terminal of SIN1 is sufficient to bind SAP1. Previous experiments defined different domains of SIN that interact with other proteins and with DNA. The C‐terminal domain of SIN1 was shown to be responsible for interaction with a protein that binds the regulatory region of HO, a gene whose transcription is repressed by SIN1. The central ‘HMG1‐like region’ of SIN1 binds DNA, while the N‐terminal of SIN1 can bind CDC23, a protein that regulates chromosome segregation. These data, taken together with the results presented here, suggest that SIN1 is a multifunctional chromatin protein that can interact with a number of different proteins that are involved in several different cellular functions.