Homeobox protein ESX1 is a protein that in humans is encoded by the ESX1 gene.

This gene 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. This gene likely plays a role in placental development and spermatogenesis. [provided by RefSeq, Jan 2010].
Function: May coordinately regulate cell cycle progression and transcription during spermatogenesis. Inhibits degradation of polyubiquitinated cyclin A and cyclin B1 and thereby arrests the cell cycle at early M phase. ESXR1-N acts as a transcriptional repressor. Binds to the sequence 5'-TAATGTTATTA-3' which is present within the first intron of the KRAS gene and inhibits its expression. ESXR1-C has the ability to inhibit cyclin turnover.