At least two of the genes predicted to encode type II PI4K (phosphoinositide 4-kinase) in Arabidopsis thaliana (thale cress), namely AtPI4Kγ4 and AtPI4Kγ7, encode enzymes with catalytic properties similar to those of members of the PIKK (phosphoinositide kinase-related kinase) family. AtPI4Kγ4 and AtPI4Kγ7 undergo autophosphorylation and phosphorylate serine/threonine residues of protein substrates, but have no detectable lipid kinase activity. AtPI4Kγ4 and AtPI4Kγ7 are members of a subset of five putative AtPI4Ks that contain N-terminal UBL (ubiquitin-like) domains. In vitro analysis of AtPI4Kγ4 indicates that it interacts directly with, and phosphorylates, two proteins involved in the ubiquitin–proteasome system, namely UFD1 (ubiquitin fusion degradation 1) and RPN10 (regulatory particle non-ATPase 10). On the basis of the present results, we propose that AtPI4Kγ4 and AtPI4Kγ7 should be designated UbDKγ4 and UbDKγ7 (ubiquitin-like domain kinases γ4 and γ7). These UBL-domain-containing AtPI4Ks correspond to a new PIKK subfamily of protein kinases. Furthermore, UFD1 and RPN10 phosphorylation represents an additional mechanism by which their function can be regulated.
Characterization of a new family of protein kinases from Arabidopsis containing phosphoinositide 3/4-kinase and ubiquitin-like domains
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Rafaelo M. Galvão, Uma Kota, Erik J. Soderblom, Michael B. Goshe, Wendy F. Boss; Characterization of a new family of protein kinases from Arabidopsis containing phosphoinositide 3/4-kinase and ubiquitin-like domains. Biochem J 1 January 2008; 409 (1): 117–127. doi: https://doi.org/10.1042/BJ20070959
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