Partitioning defective 6 homolog alpha is a protein that in humans is encoded by the PARD6A gene.

This gene is a member of the PAR6 family and encodes a protein with a PSD95/Discs-large/ZO1 (PDZ) domain and a semi-Cdc42/Rac interactive binding (CRIB) domain. This cell membrane protein is involved in asymmetrical cell division and cell polarization processes as a member of a multi-protein complex. The protein also has a role in the epithelial-to-mesenchymal transition (EMT) that characterizes the invasive phenotype associated with metastatic carcinomas. Alternate transcriptional splice variants, encoding different isoforms, have been characterized. [provided by RefSeq, Jul 2008].
Function: Adapter protein involved in asymmetrical cell division and cell polarization processes. Probably involved in the formation of epithelial tight junctions. Association with PARD3 may prevent the interaction of PARD3 with F11R/JAM1, thereby preventing tight junction assembly. The PARD6-PARD3 complex links GTP-bound Rho small GTPases to  atypical protein kinase C proteins.