Has E3 ubiquitin ligase activity towards IGBP1, promoting its monoubiquitination, which results in deprotection of the catalytic subunit of protein phosphatase PP2A, and its subsequent degradation by polyubiquitination. 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. Homodimer or heterodimer with MID2. Interacts with IGBP1. Interacts with TRIM16. Microtubule-associated. It is associated with microtubules throughout the cell cycle, co-localizing with cytoplasmic fibers in interphase and with the mitotic spindle and midbodies during mitosis and cytokinesis. In the fetus, highest expression found in kidney, followed by brain and lung. Expressed at low levels in fetal liver. In the adult, most abundant in heart, placenta and brain. A retroviral element acts as an alternative tissue-specific promoter for this gene. The LTR of an HERV-E element enhances the expression in placenta and embryonic kidney. Phosphorylated on serine and threonine residues. The disease is caused by variants affecting the gene represented in this entry. MID1 mutations produce proteins with a decreased affinity for microtubules. Belongs to the TRIM/RBCC family.