ESX Homeobox Protein 1 (ESX1)

ESX1 encodes a dual-function 65 kDa protein that undergoes proteolytic cleavage to produce a 45 kDa N-terminal fragment with a paired-like homeodomain and a 20 kDa C-terminal fragment with a proline-rich domain. The C-terminal fragment localizes to the cytoplasm while the N-terminal fragment localizes exclusively to the nucleus. In contrast to human, the mouse homolog has a novel PN/PF motif in the C-terminus and is paternally imprinted in placental tissue. The deduced 406-amino acid protein contains an N-terminal glutamic acid-rich region, followed by a central homeodomain and a C-terminal proline-rich region, which is organized into 12 contiguous repeats of a 9-amino acid motif. The homeodomains of mouse Esx1 and human ESX1L share 65% identity.