Identification of a 40 kDa Protein Kinase Activated by Stress in a Halotolerant Green Alga Dunaliella tertiolecta

Abstract

Activation of a 40 kDa protein kinase in Dunaliella tertiolecta was detected by in-gel kinase assay when the cells were subjected to various forms of stress, such as heat shock, acidic stress and H2O2. The substrate specificity of the 40 kDa kinase resembles that of HAP kinase (high osmotic pressure-activated protein kinase). An anti-phosphotyrosine monoclonal antibody did not co-precipitate with the 40 kDa kinase in the cell extracts of Dunaliella subjected to stress. Treatment of Dunaliella cells with mastoparan or AIF-4, trimeric G-protein activators, stimulated another protein kinase with a relative molecular mass of 46 kDa. This protein kinase has a different substrate specificity from that of HAP kinase and the stress-activated 40 kDa kinase. These results suggest that the stress-activated 40 kDa kinase is closely related to HAP kinase and that the 46 kDa kinase is associated with a putative trimeric G-protein. © 2002, Japanese Society of Microbial Ecology & The Japanese Society of Soil Microbiology. All rights reserved.