Speckle-type POZ protein (SPOP) belongs to the Tdpoz family containing one N-terminal MATH (Meprin and TRAF homology) domain and one C-terminal BTB/POZ domain. SPOP inhibits IPF1/PDX1 transactivation of established target promoters, such as insulin, may be by recruiting a repressor complex. SPOP is involved in ubiquitinylation and protein degradation as a result of an interaction with CUL-3.