This domain can be found in the N terminus of the bacterial SirB1 protein. It can also be found in the mammalian F-box only protein 21 (FBXO21). SirB is required for maximal expression of sirC, which encodes an SPI1-encoded transcription factor []. FBXO21 is a substrate-recognition component of the SCF (SKP1-CUL1-F-box protein)-type E3 ubiquitin ligase complex [].
