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An iron-sulfur cluster in the C-terminal domain of the p58 subunit of human DNA primase

Overview of Weiner BE et al.

AuthorsWeiner BE  Huang H  Dattilo BM  Nilges MJ  Fanning E  Chazin WJ  
AffiliationDepartment of Biochemistry   Vanderbilt University   Nashville   Tennessee   37232; Center for Structural Biology   Vanderbilt University   Nashville   Tennessee 37232; Department of Chemistry   Vanderbilt University   Nashville   Tennessee   37232. Electronic address: walter.chazin@vanderbilt.edu.  
JournalJ Biol Chem
Year 2007

Abstract


DNA primase synthesizes short RNA primers that are required to initiate DNA synthesis on the parental template strands during DNA replication. Eukaryotic primase contains two subunits, p48 and p58, and is normally tightly associated with DNA polymerase alpha. Despite the fundamental importance of primase in DNA replication, structural data on eukaryotic DNA primase are lacking. The p48/p58 dimer was subjected to limited proteolysis, which produced two stable structural domains: one containing the bulk of p48 and the other corresponding to the C-terminal fragment of p58. These domains were identified by mass spectrometry and N-terminal sequencing. The C-terminal p58 domain (p58C) was expressed, purified, and characterized. CD and NMR spectroscopy experiments demonstrated that p58C forms a well folded structure. The protein has a distinctive brownish color, and evidence from inductively coupled plasma mass spectrometry, UV-visible spectrophotometry, and EPR spectroscopy revealed characteristics consistent with the presence of a [4Fe-4S] high potential iron protein cluster. Four putative cysteine ligands were identified using a multiple sequence alignment, and substitution of just one was sufficient to cause loss of the iron-sulfur cluster and a reduction in primase enzymatic activity relative to the wild-type protein. The discovery of an iron-sulfur cluster in DNA primase that contributes to enzymatic activity provides the first suggestion that the DNA replication machinery may have redox-sensitive activities. Our results offer new horizons in which to investigate the function of high potential [4Fe-4S] clusters in DNA-processing machinery.