Has negligible PIP5 kinase activity. Binds to ubiquitinated proteins. Testis-specific. PIPSL gene appeared in hominoids by L1-mediated retrotransposition in a hominoid ancestor of a readthrough, intergenically spliced transcript between the PIP5K1A and PSMD4 genes. Could be the product of a pseudogene. Although transcribed, the gene is poorly translated probably due to a deletion in the regulatory region. PubMed:17623810 could not detect the protein by Western blot.