Fission yeast Pik1p is one of three phosphatidylinositol 4-kinases associated with the Golgi complex, but its function is not fully understood. Deletion of pot1(+) causes telomere degradation and chromosome circularization. We searched for the gene which becomes synthetically lethal with pot1 Delta. We obtained a novel pik1 mutant, pik1-1, which is synthetically lethal with pot1 Delta. We found phosphoinositol 4 phosphate in the Golgi was reduced in pik1-1. To investigate the mechanism of the lethality of the pot1 Delta pik1-1 double mutant, we constructed the nmt-pot1-aid pik1-1 strain, where Pot1 function becomes low by drugs, which leads to telomere loss and chromosome circularization, and found pik1-1 mutation does not affect telomere resection and chromosome circularization. Thus, our results suggest that pik1(+) is required for the maintenance of circular chromosomes. (C) 2018 Elsevier Inc. All rights reserved.