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As all the TIF1 proteins, KAP-1 owns a N-terminal tripartite motif (TRIM). This motif is a protein-protein interface which contains an RBCC domain (itself composed of a Ring finger, two B-box zinc fingers, and a coiled-coil domain) and a central TIF1 signature sequence (TSS). KAP-1 has a C-terminal motif composed of one homeodomain (PHD) and one bromodomain. Moreover, KAP-1 possesses a central binding domain called HP1 (for heterochromatin protein 1). | As all the TIF1 proteins, KAP-1 owns a N-terminal tripartite motif (TRIM). This motif is a protein-protein interface which contains an RBCC domain (itself composed of a Ring finger, two B-box zinc fingers, and a coiled-coil domain) and a central TIF1 signature sequence (TSS). KAP-1 has a C-terminal motif composed of one homeodomain (PHD) and one bromodomain. Moreover, KAP-1 possesses a central binding domain called HP1 (for heterochromatin protein 1). | ||
As said before, the fisrt part of KAP-1 is the N-Terminal motif, within we can find the RBCC sequence. The RBCC domain has a high affinity for protein interactions. Thus, this is the RBCC domain which alllows the interaction between KAP-1 and the 3 -ends of ZNF genes of KRAB-ZNFs domains. In this way, KAP-1 binds as a homotrimer to a single KRAB domain. There is then an oligomerization which provides folding of the KRAB domain to encapsulates it in a protease-resistant core. RBCC is composed of three subdomains. One of these is the ring subdomain. This is a double zinc-binding | As said before, the fisrt part of KAP-1 is the N-Terminal motif, within we can find the RBCC sequence. The RBCC domain has a high affinity for protein interactions. Thus, this is the RBCC domain which alllows the interaction between KAP-1 and the 3 -ends of ZNF genes of KRAB-ZNFs domains. In this way, KAP-1 binds as a homotrimer to a single KRAB domain. There is then an oligomerization which provides folding of the KRAB domain to encapsulates it in a protease-resistant core. RBCC is composed of three subdomains. One of these is the ring subdomain. This is a double zinc-binding C3 <sup>3</sup>HC4 motif. The second subdomain is composed of the two B-box which are cysteine-rich zinc-binding motif of the form CHC3H2. These latter interacts with the last subdomain : the coiled-coil domain. These two subdomains form an extended hydrophobic helical region. It’s here that protein-protein interactions take place. Next to the RBCC motif, there is the TSS sequence which is tryptophan and phenylalanine rich. We know that the deletion of this sequence cancel the transcriptional repression mediated by TIF1γ. | ||
Between the N-Terminal and the C-Terminal motif, KAP-1 owns a HP1 binding domain which is a hydrophobic PxVxL pentapeptide. This pentapeptide allows the interaction of KAP-1 with the chromoshadow domain of all the proteins of the HP1 family. This is necessary for the repression of reporter genes. This domain is proline, glycine and serine rich. | Between the N-Terminal and the C-Terminal motif, KAP-1 owns a HP1 binding domain which is a hydrophobic PxVxL pentapeptide. This pentapeptide allows the interaction of KAP-1 with the chromoshadow domain of all the proteins of the HP1 family. This is necessary for the repression of reporter genes. This domain is proline, glycine and serine rich. | ||