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Functional and structural studies of the regulatory proteins Ki-1/57 and cgi-55 and interacting protein partners


The 57 kDa protein antigen (Ki-1/57) was first isolated from malignant Hodgkin cells. Preliminary functional and molecular biological studies had indicated that this protein has features typical for many oncoproteins, like e.g. elevated expression in tumor versus normal cells, cell activation dependent expression, cytoplasmatic-nuclear shutteling, phosphorylation on serine/threonine residues and association with protein kinase activity. In order to better understand the functional biological context of this protein as well of its putative paralog protein CGI-55 (63% sequence similarity) we performed "yeast two hybrid" screens to identify their interacting protein partners. We were able to demonstrate that both proteins have interacting proteins in common but also unique interacting partners. In the case of CGI-55 the great majority of interacting proteins were nuclear proteins that are associated with functions such as the regulation of gene expression (hPc2, Topors, DAXX, PIAS) and the remodeling of chromatin (CHD-3, Topors). Ki-1/57 interacted aside from CHD-3 and Topors also with several cytoplasmic proteins that are involved in signal transduction cascades, like e.g. RACK-1 and HRMTL. In the project proposed here we want to continue to study the function and structure of the proteins Ki-1/57 and CGI-55 as well as its interacting proteins by molecular biological and cell biological methods. A special focus of the functional studies will be on protein-phosphorylation, -methylation and signal transduction, while the structural studies will address both the individual proteins as well as possible complexes of the interacting proteins (e.g. Ki-1/57 and RACK-1) to contribute to our understanding of the specificity of protein interactions. (AU)

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