Fig. 1. Evolutionary conservation of the Citron Kinase family of proteins. (A) The family of Drosophila proteins containing the same conserved domains as vertebrate Citron. Each line is a scale representation of the protein sequence (scale bar represents 100 amino acids), with each conserved domain marked as a different shape. S/T Kinase, protein kinase C-class Serine/Threonine kinase domain; C1, protein kinase C-type diacylglycerol binding domain; PH, Pleckstrin homology phospholipid binding domain; CNH, Citron homology domain of unknown function; PBD, p21-like Cdc42 binding domain. Numbers between the conserved domains indicate the percentage of amino acid identity between the corresponding domains. Arrowed lines indicate the regions known to be required for binding to Rho. (B) A C-terminal fragment of Citron (Citron 4, amino acids 1439 to 1854) interacts specifically with constitutively active RhoA-G14V. LexA-Citron fusion proteins 1 to 4, represented by the lines below the domain structure of Citron in A, were assayed for interaction with VP16-RhoA-G14V fusion protein by activation of a lacZ reporter gene in a yeast two-hybrid assay. The strength of interaction is indicated to the right of each Citron fragment, with (–) indicating no interaction and (+++) indicating a strong interaction.