UspA, the Universal Stress Protein of Stimulates the Activity of the PP2A Phosphatase and Is Involved in Growth at High Salinity.

In , the protein phosphatase PP2A plays important regulatory roles in many cellular processes, including cell growth, cell shape and synthesis of the archaellum. A conserved prokaryotic protein, designated as UspA, was identified as an interaction partner of the phosphatase PP2A. UspA belongs to the universal stress protein (USP) superfamily, members of which are found in bacteria, archaea, plants and invertebrates. Biochemical analysis showed that UspA is a homodimeric ATP-binding protein, which also binds to PP2A. UspA did not hydrolyze ATP, but stimulated the phosphatase activity of PP2A and might in this manner affect many other processes. Interestingly, binding of ATP further enhanced UspA's interaction with PP2A. In contrast to bacterial genes, environmental stress conditions including stationary phase, starvation stress, high salinity stress and UV stress did not stimulate expression of . Deletion of led to premature production of the archaellin FlaB in although motility was not affected. The Δ mutant showed a significant growth defect under high salinity stress and complementation of ATP-binding deficient mutant UspA failed to restore this growth defect. Compared with the wild type strain, its growth or survival was not affected under heavy metal stress and UV stress. To date, this is the first study in which the physiological role of USP homologs in archaea have been reported.