Acts on phosphatidylinositol (PtdIns) in the first committed step in the production of the second messenger inositol-1,4,5,-trisphosphate. a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol) + ATP = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + ADP + H(+) Activated by Triton X-100, insensitive to inhibition by adenosine and inhibited by wortmannin (By similarity). Isoform 2 is activated by detergents such as Triton X-100 and inhibited by adenosine (PubMed:7961848). The PI4K complex acts as a regulator of phosphatidylinositol 4-phosphate (PtdIns(4)P) synthesis (PubMed:23229899, PubMed:26571211). Interaction with TMEM150A regulates PtdIns(4)P synthesis (PubMed:25608530). Component of a phosphatidylinositol 4-kinase (PI4K) complex, composed of PI4KA, EFR3 (EFR3A or EFR3B), TTC7 (TTC7A or TTC7B) and FAM126 (FAM126A or FAM126B) (PubMed:23229899, PubMed:24417819, PubMed:26571211, PubMed:34415310). Interacts with TMEM150A; regulating recruitment to the plasma membrane (PubMed:25608530). Interacts with TTC7A (PubMed:34415310). (Microbial infection) Interacts with CHKA/Choline Kinase-alpha; CHKA bridges PI4KA and hepatitis C virus (HCV) non-structural protein 5A (NS5A) and potentiates NS5A-stimulated PI4KA activity, which then facilitates the targeting of the ternary complex to the ER for viral replication. Localization to the plasma membrane is mediated by the PI4K complex and association with EFR3 (EFR3A or EFR3B), TTC7 (TTC7A or TTC7B) and FAM126 (FAM126A or FAM126B) (PubMed:23229899). Localization to the plasma membrane is regulated by TMEM150A (PubMed:25608530). Expressed ubiquitously. Highest levels in placenta and brain. Little or no expression in lung, liver, pancreas, testis or leukocytes. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the PI3/PI4-kinase family. Type III PI4K subfamily.