An internal region of the RpoH heat shock transcription factor is criticalfor rapid degradation by the FtsH protease

The proteolysis of regulatory proteins plays an important role in the contr ol of gene expression. The Escherichia coli heat shock sigma factor RpoH (s igma (32)) is highly unstable, Its instability is determined by interaction s with the DnaK chaperone machine, RNA polymerase and the ATP-dependent pro tease FtsH. Bradyrhizobium japonicum expresses three RpoH proteins of which RpoH(1) is highly stable. To determine which regions of E. coli RpoH deter mine protein lability, we generated a number of truncated versions and hybr id proteins. Truncation of N-terminal amino acids had no, and deletion of C -terminal amino acids only a minor effect on stability of RpoH, A major det erminant of RpoH lability was mapped to a region of about 85 amino acids (r esidues 36-122) roughly comprising the sigma factor region 2, This is the f irst demonstration of an internal RpoH region being responsible for FtsH-me diated degradation. (C) 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.