Partitioning defective 3 homolog is a protein in humans that is encoded by PARD3 gene. Partitioning defective 3 homolog is a protein that in humans is encoded by the PARD3 gene. PARD proteins, which were first identified in C. elegans, are essential for asymmetric cell division and polarized growth, whereas CDC42 (MIM 116952) mediates the establishment of cell polarity. The CDC42 GTPase, which is controlled by nucleotide exchange factor and GTPase-activating proteins, interacts with a large set of effector proteins that typically contain a CDC42/RAC-interactive binding (CRIB) domain.