Molecular dissection of a protein SopB essential for Escherichia coli F plasmid partition.
Biochemical and genetic experiments were carried out to deduce the structural and functional domains of SopB protein involved in the equipartition of F plasmid. The protein is dimeric. Proteolytic and chemical footprinting studies support earlier genetic analyses that the binding of SopB to specific sites within the F plasmid sopC locus involves mainly the C-terminal region. In vivo, the expression of a high level of SopB protein is known to repress sopC-linked genes. This silencing activity is shown to be unaffected by the deletion of 35 N-terminal residues, but abolished when 71 or more were removed from the N terminus. An excess of SopB protein does not extend its in vitro binding outside sopC, implicating participation of a host factor(s) in SopB-mediated gene silencing. A data base search identified a number of SopB homologues, including both chromosomally encoded bacterial proteins and phage- and plasmid-encoded proteins known to be involved in partition. Sequence homology is limited to the N-terminal half, suggesting that the N-terminal regions of these proteins are conserved to interact with a conserved cellular structure(s), whereas the C-terminal regions have diverged to bind different nucleotide sequences.
Hanai
R
R
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Liu
R
R
Benedetti
P
P
Caron
P R
PR
Lynch
A S
AS
Wang
J C
JC
D000595:Amino Acid Sequence; D001419:Bacteria / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005144:F Factor / Q000378:metabolism / Q000648:ultrastructure; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C060972:SopB protein, Bacteria; C489223:SopB protein, E coli