Sex-determining factor that is required for sexual differentiation and X chromosome dosage compensation to promote male development (PubMed:7813020, PubMed:9217163, PubMed:33372658). High expression during gastrulation triggers male development, while low expression at that time triggers hermaphrodite development. Although related to GHMP kinase, its mode of action remains unclear. Specifically expressed at high levels in pre-comma stage XO embryos. Also present at low levels throughout other larval stages in XO animals, but are nearly undetectable in XX larvae and adults of both sexes. Most abundant in male embryos (PubMed:33372658). Expressed at low levels in hermaphrodite embryos (PubMed:33372658). Down-regulated by at least 4 X-linked genes, termed X-signal elements including fox-1 and sex-1 (PubMed:9217163). High levels of xol-1 in males correlate with low sdc-2 expression, preventing dosage compensation. Conversely, low levels of xol-1 in hermaphrodites correlate with high sdc-2 expression and the assembly of the dosage compensation complex on the X chromosome. Worms are XO-lethal, due to inappropriate activating dosage compensation where only 1 X chromosome is present. In contrast xol-1 overexpression is XX-lethal, deactivating the dosage compensation pathway and elevating the expression of X chromosome genes to lethal levels in hermaphrodites. Only functional isoform (PubMed:33372658). Produced by alternative splicing of intron 6 which results in the deletion of intron 6 and retention of exon 7 coding sequences (PubMed:33372658). Inactive isoform (PubMed:7813020, PubMed:33372658). Produced by alternative splicing of intron 6 which results in the retention of intron 6 and deletion of exon 7 coding sequences (PubMed:33372658). An in-frame UAA stop codon within intron 6 prematurely terminates translation (PubMed:7813020). Intron 6 retention and exon 7 deletion can also be due to use of an alternative 3' splice acceptor site in the 3'UTR resulting in trans-splicing to the transcripts of unrelated genes (PubMed:33372658). Belongs to the GHMP kinase family. Xol-1 subfamily. Although clearly related the GHMP kinase family as demonstrated by the 3D-structure, it lacks many conserved feature of GHMP kinases and probably does not bind ATP, suggesting that it probably does not have kinase activity.