Phosphorylates the splicing regulator TIA1, thereby promoting the inclusion of FAS exon 6, which leads to an mRNA encoding a pro- apoptotic form of the receptor. {ECO:0000269|PubMed:17135269, ECO:0000269|PubMed:7544399}. [Isoform 4]: Required for the biogenesis of some mitochondrial-encoded mRNAs, specifically stabilizes ND6 (NADH dehydrogenase complex subunit 6) mRNA, and regulates its levels. . This is the function of Ensembl gene identifier ENSG00000164896 (FASTK, Fas activated serine/threonine kinase).