Arch Microbiol (2009) 191:185–190
DOI 10.1007/s00203-008-0441-z
123
SHORT COMMUNICATION
Role of single-strand DNA 3Ј-5Ј exonuclease ExoI and nuclease
SbcCD in stationary-phase mutation in Escherichia coli K-12
Jesús Ramírez-Santos · Verónica García-Mata ·
Sebastian Poggio · Laura Camarena ·
M. Carmen Gómez-Eichelmann
Received: 3 July 2008 / Revised: 2 September 2008 / Accepted: 13 October 2008 / Published online: 19 November 2008
© Springer-Verlag 2008
Abstract In RecBCD
+
cells, a mutated single-strand
DNA 3Ј-5Ј exonuclease ExoI (SbcB15) induced an increase
in stationary-phase mutation. In sbcB15 cells, as in wild-
type cells, these mutations partially required RecA, RecB,
RecF, and expression of the LexA regulon. The absence of
nuclease SbcCD in sbcB15 cells decreased stationary-phase
mutation and induced an increase in the number of cell Wla-
ments. The absence of ExoI (xon) in wild-type or sbcC
cells did not change signiWcantly the stationary-phase
mutation. DiVerences between the sbcB15 and xonA cells
suggest a correlation between level of SOS induction and
the generation of stationary-phase mutations.
Keywords Escherichia coli · ssDNA exonuclease I ·
Nuclease SbcCD · Stationary-phase mutation
Introduction
The stationary-phase, or adaptive mutations (SM), exten-
sively studied in Escherichia coli (Foster 2007; Galhardo
et al. 2007), and documented in other bacteria and yeast
(Heidenreich 2007; Robleto et al. 2007), are generated by
mutagenic processes diVerent from those observed in grow-
ing cells. The main assay used to study the SM phenome-
non in E. coli, measures the reversion rate of a lac +1
frameshift mutation carried on a conjugative FЈ plasmid
(Cairns and Foster 1991). Two main pathways have been
proposed for the generation of SM in E. coli: point muta-
tion, and DNA ampliWcation. The Wrst pathway accounts
for most mutations, involves the presence of DNA double-
strand breaks (DSBs) or DNA double-strand ends (DSE) as
the main DNA damage in starved cells, and error-prone
repair by homologous recombination (HR) of this damage
(Foster 2007; Galhardo et al. 2007). DSB could be gener-
ated by restriction enzymes, and enzymes not yet known,
and DSE by stalled and regressed replication forks (Rosen-
berg 2001). The error-prone repair requires proteins RecA,
RecBCD, RecF, RuvABC and the LexA-, RpoS-controlled
error-prone DNA polymerase IV (PolIV) (Cairns and Fos-
ter 1991; Harris et al. 1994, 1996; Foster et al. 1996;
McKenzie et al. 2000, 2001
; Layton and Foster 2003; He
et al. 2006). SM generation also depends on the expression
of other RpoS- and LexA-controlled proteins, and of FЈ
plasmid-encoded proteins (Foster and Trimarchi 1995;
Layton and Foster 2003; Ponder et al. 2005). The induction
of the SOS LexA regulon necessary to favor the generation
of SM seems to be within a narrow range in the continuum
of SOS induction levels (McKenzie et al. 2000). The sec-
ond pathway involves ampliWcation of the leaky lac mutant
allele, does not require SOS induction and PolIV, and
produces approximately 2–10% of the Lac
+
revertants
(Hastings et al. 2000; McKenzie et al. 2001).
It is known that mutations in recA, recBC, ruvABC,
recF, lexA and dinB (PolIV) decrease SM, while mutations
in genes for RecD, a component of the helicase-nuclease
RecBCD, and for the single-strand (ss) DNA exonucleases
5Ј-3Ј RecJ, and 3Ј-5Ј ExoI (SbcB) increase these mutations
(Harris et al. 1994, 1996; Foster and Rosche 1999; Bull
et al. 2001). The tested mutated allele of sbcB was xonA300
(Foster and Rosche 1999). RecBCD is a multifunctional
Communicated by Jorge Membrillo- Hernandez.
J. Ramírez-Santos · V. García-Mata · S. Poggio · L. Camarena ·
M. C. Gómez-Eichelmann (&)
Departamento de Biología Molecular y Biotecnología,
Instituto de Investigaciones Biomédicas,
Universidad Nacional Autónoma de México,
P.O. Box 70-228, 04510 Mexico, D.F., Mexico
e-mail: cargom@servidor.unam.mx