Trabajo

Vol. 52 No. 1/2005
1–34
QUARTERLY

Review

Bacterial chromosome segregation
Aneta A. Bartosik and Grażyna Jagura-Burdzy½
Department of Microbial Biochemistry, Institute of Biochemistry and Biophysics, Polish
Academy of Sciences, Warszawa, Poland
Received: 25 January, 2005; 28 February, 2005
Key words: bacterial cell cycle, chromosome replication and segregation, factory model,
sistercohesion model, proteins engaged in chromosome partitioning
In most bacteria two vital processes of the cell cycle: DNA replication and chromosome segregation overlap temporally. The action of replication machinery in a fixed
location in the cell leads to the duplication of oriC regions, their rapid separation to
the opposite halves of the cell and the duplicated chromosomes gradually moving tothe same locations prior to cell division. Numerous proteins are implicated in
co-replicational DNA segregation and they will be characterized in this review. The
proteins SeqA, SMC/MukB, MinCDE, MreB/Mbl, RacA, FtsK/SpoIIIE playing different roles in bacterial cells are also involved in chromosome segregation. The chromosomally encoded ParAB homologs of active partitioning proteins oflow-copy number
plasmids are also players, not always indispensable, in the segregation of bacterial
chromosomes.

In prokaryotes, the essential genetic information is usually carried on a single circular
chromosome, although linear (Jakimowicz et
al., 2002) and multi-replicon genomes — containing more than one chromosome (Kolsto,
½

1999; Suwanto & Kaplan, 1992; Jumas-Bilak
et al., 1998) —have been found in some bacteria. During the bacterial cell cycle chromosomes are duplicated and segregated into
daughter cells.

Correspondence to: G. Jagura-Burdzy, Department of Microbial Biochemistry, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, A. Pawińskiego 5a, 02-106 Warszawa, Poland; G.J-B.
tel.: (48 22) 823 7192; e-mail: gjburdzy@ibb.waw.pl; A.A.B. tel.: (48 22)659 1216; e-mail:
anetab2@ibb.waw.pl
Abbreviations: FISH, fluorescence in situ hybridization; GFP, green fluorescent protein; PAR, partitioning protein; RAC, remodelling and anchoring of the chromosome; RTP, sequence-specific termination protein; SMC, structural maintenance of chromosome; SSB, single-stranded DNA binding protein.

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A.A. Bartosik and G. Jagura-Burdzy

In eukaryoticcells, chromosome replication,
segregation and cell division are separated in
time. Chromosomes are duplicated in S phase
and remain together during G2 phase. Partitioning occurs in M phase and then the cell divides after the chromosomes have segregated
to opposite halves of the cell. The G1 phase is
the period from the end of cell division to the
beginning of the S phase. The eukaryoticcell-cycle nomenclature has been applied to
bacteria with some modifications (Helmstetter, 1996). The DNA synthesis phase (S)
corresponds to the C period in bacteria and
the period from the completion of replication
to the end of cell division (G2-M) is the D period. G1 is the period from the separation of
newly formed daughter cells to the beginning
of C phase.
In Caulobacter crescentus and inmany other
slow-growing bacteria the G1, C and D periods
are temporally separated as in eukaryotes
(Helmstetter, 1996; Sherratt, 2003). In fast
growing bacteria two or more cycles of chromosome replication may overlap (generation
time is shorter than the C+D period) and before the newly replicated chromosomes have
been segregated to daughter cells the next
rounds of replication areinitiated. Thus, the
newly formed daughter cells have at least two
oriC replication origins, located in the opposite halves of the cell, and about 50% of the
chromosome already replicated (Lau et al.,
2003). In contrast to eukaryotic cells, chromosome segregation and cell division in fast
growing bacteria occur while chromosomes
undergo replication. Nevertheless, DNA replication and segregation...