JB Accepts, published online ahead of print on 1 September 2006

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J. Bacteriol. doi:10.1128/JB.00943-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Post-translational modification of the 20S proteasomal proteins of the archaeon Haloferax volcanii

Matthew A. Humbard, Stanley M. Stevens Jr., and Julie A. Maupin-Furlow^*

University of Florida, Department of Microbiology and Cell Science, Gainesville, Florida 32611-0700, USA; University of Florida, Proteomics Core Facility, ICBR, Gainesville, Florida 32610-0156, USA

^* To whom correspondence should be addressed. Email: jmaupin{at}ufl.edu.

20S proteasomes are large, multicatalytic proteases that play an important role in intracellular protein degradation. The architecture of 20S proteasomes is highly conserved from archaea to eukaryotes and is barrel-like, formed by the stacking of four heptameric protein rings. The outer two rings are composed of -type subunits, and the inner two rings are composed of -type subunits. The halophilic archaeon Haloferax volcanii synthesizes two different -type proteins, 1 and 2, and one -type protein which assemble into at least two 20S proteasome subtypes. In this study, we demonstrate that all three of these 20S proteasomal proteins (1, 2, and ) are modified either post- or co-translationally. Using electrospray ionization quadrupole time-of-flight mass spectrometry, a phosphorylation site of the subunit was identified at Ser129 of the deduced protein sequence. In addition, 1 and 2 contained N-terminal acetyl groups. These findings represent the first evidence of acetylation and phosphorylation of archaeal proteasomes and are one of the limited examples of post- and/or co-translational modification of proteins in this unusual group of organisms.

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