SMER3 is a selective inhibitor of Skp1-Cullin-F-box (SCF)MET30 ubiquitin ligase, an E3 ligase that regulates transcription, cell-cycle control, and immune response. It is a small molecule enhancer of rapamycin , in that it enhances yeast cell lethality in response to rapamycin. SMER3, at 5 μM, upregulates a set of methionine biosynthesis genes by altering the SCFMET30 complex, preventing ubiquitination of target proteins, including Met4. As ubiquitin E3 ligases are involved in tumorigenesis, SMER3 has potential applications in cancer research.