Display Settings:


Send to:

Choose Destination
See comment in PubMed Commons below
J Bacteriol. 1999 Oct;181(19):6033-41.

A mutant HemA protein with positive charge close to the N terminus is stabilized against heme-regulated proteolysis in Salmonella typhimurium.

Author information

  • 1Department of Microbiology and Immunology, West Virginia University Health Sciences Center, Morgantown, West Virginia 26506, USA.


The HemA enzyme (glutamyl-tRNA reductase) catalyzes the first committed step in heme biosynthesis in the enteric bacteria. HemA is mainly regulated by conditional protein stability; it is stable and, consequently, more abundant in heme-limited cells but unstable and less abundant in normally growing cells. Both the Lon and ClpAP energy-dependent proteases contribute to HemA turnover in vivo. Here we report that the addition of two positively charged lysine residues to the third and fourth positions at the HemA N terminus resulted in complete stabilization of the protein. By contrast, the addition of an N-terminal myc epitope tag did not affect turnover. This result confirms the importance of the N-terminal sequence for proteolysis of HemA. This region of the protein also contains a proline flanked by hydrophobic residues, a motif that has been suggested to be important for Lon-mediated proteolysis of UmuD. However, mutation of this motif did not affect the turnover of HemA protein. Cells expressing the stabilized HemA[KK] mutant protein display substantial defects in heme regulation.

[PubMed - indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk