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Summary: The filament (shown in Fig. 3A as a linear
structure for simplicity) is more likely to be
compacted in a solenoid in which the DNA
wraps through multiple turns about a protein
core, as was suggested by the observed
changes in linking numbers upon formation
of a SopB-DNA complex (19).
Prokaryotic centromeres are characterized
by the presence of arrays of sites to which
one of the partition proteins bind. There are 6
sites in P1 (Fig. 1A), 12 in F, 10 in R1, and 12
in pTAR (20). Whereas these plasmid-borne
binding sites are tightly clustered, the several
chromosomal binding sites for the Bacillus
subtilis partition (and sporulation) protein
Spo0J are distributed over a region spanning
many kilobases (3). The centromere may
serve as a handle that is used to tether or
orient a large structure, with its several bind-
ing sites facilitating a steady grip or the for-
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