E3 ubiquitin ligase catalyzing the covalent attachment of ubiquitin moieties onto substrate proteins. These substrates include FILIP1, p53/TP53, CDKN1A and TERT. Keeps cells alive by suppressing p53/TP53 under normal conditions, but stimulates apoptosis by repressing CDKN1A under stress conditions. Acts as a negative regulator of telomerase (By similarity). Has negative and positive effects on RNA polymerase II-dependent transcription. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with p53/TP53 and CDKN1A. Interacts with TERT, modulating telomere length homeostasis (By similarity). Highly expressed in embryo, in specific cell types of the central nervous system, in brain with the strongest levels of expression in the mantle layers and in testis. Moderate to low levels in somatic tissues. Not detected until 11 dpc. Restricted to developing central nervous system in 13 days embryos. Auto-ubiquitinated; which leads to proteasomal degradation. PubMed:12968785 describes 80 % of lethality within 2 days of birth in heterozygotes and polycystic kidney and bone deformity in survivors. However, PubMed:16882727 reports no apparent developmental deficits with viable and fertile mice. PubMed:12968785 shows that the expression of the transcribed processed pseudogenes (TPP) Makorin1-p1 prevents the decay of functional Mkrn1 mRNAs. In contrast, PubMed:16882727 shows that Makorin1-p1 is not transcribed and that the putative transcripts represent an alternative isoform of the Mkrn1 source gene.