Figure 2(A) The N-lobe kinase linker region of PI4KB is strongly conserved back to D. rerio. The N-lobe linker region of PI4KB sequences of the organisms indicated were analysed using Clustal Omega/ ESpript 3. The consensus PKA motif (RRXS) that is conserved back to D. rerio is indicated on the sequence, as well as the RL494EA point mutation. (B) The N-lobe kinase linker of PI4KB can be efficiently phosphorylated by PKA. Recombinant PKA at different concentrations (0, 7, 34, 168, or 840 ng) was incubated with recombinant (E. coli) wild-type PI4KB (20 μg) for 1 hour with 200 μM ATP and the amount of phosphorylation was followed using mass spectrometry. Relative abundance of Ser496 phosphorylated PI4KB was calculated using the relative intensity (total area) of the phosphorylated vs non-phosphorylated peptide (486-506). (C) PI4KB phosphorylation by PKA alters the affinity for c10orf76. The kinase activity of different variants of PI4KB (15 nM) was measured in the presence of varying amounts of c10orf76 (23 nM-1.5μM) with 100% PI lipid substrate (0.5 mg/L) and 100 μM ATP. The data was normalized to the kinase activity of PI4KB alone Error bars represent standard deviation of independent technical replicates (n=3). (D) PI4KB has the same kinase activity when Ser496 is phosphorylated or mutated to alanine. Kinase assay of PI4KB non-phosphorylated, phos-Ser496 or S496A (15 nM) on pure PI lipid vesicles (0.5 mg/L) with 100 μM ATP. The data was normalized to the kinase activity of WT PI4KB. Error bars represent standard deviation of independent technical replicates (n=3). (E) Engineered RL494EA PI4KB mutant shows decreased binding to c10orf76. His-pulldown assays of 6xHis-c10orf76 (3 μM) with wild-type or RL494EA PI4KB (1-2 μM). (F) RL494EA PI4KB activity is not inhibited by c10orf76. Kinase assays of either wild type or mutant RL494EA PI4KB (40 nM) were carried out with varying concentrations of c10orf76 (3.9 nM-2μM) with 100% PI lipid vesicles (0.5 mg/L) and 100 μM ATP. The data was normalized to the kinase activity of PI4KB alone. Error bars represent standard deviation of independent technical replicates (n=3). (G) Wild-type PI4KB and RL494EA PI4KB mutant have the same lipid kinase activity. Kinase assays of either wild-type and mutant PI4KB (10 nM) were carried out with 100% PI lipid vesicles (0.5 mg/L), 100 μM ATP, and PI4KB (300 nM) on Golgi-mimic vesicles (0.5 mg/mL) with 10 μM ATP. The data was normalized to the kinase activity of WT PI4KB. Error bars represent standard deviation of independent technical replicates (n=3). (H) FLH409AAA-c10orf76 mutant shows decreased affinity for PI4KB. His-pulldown assays of 6xHis-c10orf76 (1 μM) with wild-type PI4KB (1 μM). Samples washed a total of 4 times. (I) Kinase assay shows FLH409AAA c10orf76 inhibition of PI4KB is greatly reduced. Kinase assay of PI4KB (40 nM) and a concentration curve of c10orf76 (3.9 nM-2μM) on pure PI lipid vesicles (0.5 mg/L) with 100 μM ATP. The data was normalized to the kinase activity of PI4KB alone. Error bars represent standard deviation of independent technical replicates (n=3). (J) The PI4KB-binding region of c10orf76 is strongly conserved back to D. rerio. Clustal Omega/ ESpript 3 alignment of the FLH409 region of c10orf76 that binds PI4KB.