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J. Bacteriol., 04 1997, 2426-2432, Vol 179, No. 7
J Majka, W Messer, H Schrempf and J Zakrzewska-Czerwinska
The Streptomyces lividans DnaA protein (73 kDa) consists, like the
Escherichia coli DnaA protein (52 kDa), of four domains. The larger size of
the S. lividans protein is due to an additional stretch of 120
predominantly acidic amino acids within domain II. The S. lividans protein
was overproduced as a His-tagged fusion protein. The purified protein
(isoelectric point, 5.7) has a weak ATPase activity. By DNase I
footprinting studies, each of the 17 DnaA boxes (consensus sequence,
TTGTCCACA) in the S. lividans oriC region was found to be protected by the
DnaA fusion protein. Purified mutant proteins carrying a deletion of the
C-terminally located helix-loop-helix (HLH) motif or with amino acid
substitutions in helix A (L577G) or helix B (R595A) no longer interact with
DnaA boxes. A substitution of basic amino acids in the loop of the HLH
motif (R587A or R589A) entailed the formation of S. lividans mutant DnaA
proteins with little or no capacity for binding to DnaA boxes. Thus, like
in E. coli, the C-terminally located domain IV is absolutely necessary for
the specific binding of DnaA. A mutant protein lacking a stretch of acidic
amino acids corresponding to domain II is not affected in its DNA binding
capacity. Whether the acidic domain II interacts with accessory proteins
remains to be elucidated.
Copyright © 1997, American Society for Microbiology
Purification and characterization of the Streptomyces lividans initiator protein DnaA
Ludwik Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Wroclaw.
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