E3 ubiquitin-protein ligase Praja1 is an enzyme that in humans is encoded by the PJA1 gene.

This gene encodes an enzyme that has E2-dependent E3 ubiquitin-protein ligase activity. This enzyme belongs to a class of ubiquitin ligases that include a RING finger motif, and it can interact with the E2 ubiquitin-conjugating enzyme UbcH5B. This gene is located in an area of chromosome X where several X-linked mental retardation disorders have been associated, and it has also been found as part of a contiguous gene deletion associated with craniofrontonasal syndrome, though a direct link to any disorder has yet to be demonstrated. Alternative splicing results in multiple transcript variants. [provided by RefSeq, May 2010].
Function: Has E2-dependent E3 ubiquitin-protein ligase activity. Ubiquitinates MAGED1 antigen leading to its subsequent  degradation by proteasome (By similarity). May be involved in protein sorting.