For instance, p30 was shown to up-regulate the expression of Ubc9, which leads to a decrease in the p42/p30 ratio via addition of small ubiquitin-like modifier proteins (sumoylation) and subsequent down-regulation of p42 in leukemia cells.[38] The resulting block in myeloid differentiation could be reversed by siRNA-mediated knockdown of Ubc9 and restoration of p42 levels. This evidence concerns the gene UBE2I and leukemia.