The function of ESX1 (ESX homeobox 1, Ensembl gene identifier ENSG00000123576) is as follows. 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. {ECO:0000269|PubMed:15235584, ECO:0000269|PubMed:15897875}.