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Extremophiles (2018) 22:581–589
https://doi.org/10.1007/s00792-018-1018-7
ORIGINAL PAPER
The Sulfolobus solfataricus RecQ‑like DNA helicase Hel112 inhibits
the NurA/HerA complex exonuclease activity
Mariarosaria De Falco
1
· Federica Massa
1
· Mosè Rossi
1
· Mariarita De Felice
1
Received: 22 December 2017 / Accepted: 21 February 2018 / Published online: 27 February 2018
© Springer Japan KK, part of Springer Nature 2018
Abstract
ATPase/Helicases and nucleases play important roles in DNA end-resection, a critical step during homologous recombina-
tion repair in all organisms. In hyperthermophilic archaea the exo-endonuclease NurA and the ATPase HerA cooperate with
the highly conserved Mre11-Rad50 complex in 3′ single-stranded DNA (ssDNA) end processing to coordinate repair of
double-stranded DNA breaks. Little is known, however, about the assembly mechanism and activation of the HerA-NurA
complex. In this study we demonstrate that the NurA exonuclease activity is inhibited by the Sulfolobus solfataricus RecQ-
like Hel112 helicase. Inhibition occurs both in the presence and in the absence of HerA, but is much stronger when NurA
is in complex with HerA. In contrast, the endonuclease activity of NurA is not affected by the presence of Hel112. Taken
together these results suggest that the functional interaction between NurA/HerA and Hel112 is important for DNA end-
resection in archaeal homologous recombination.
Keywords DNA repair · Homologous recombination · Nuclease · DNA helicase · Archaea · Sulfolobus solfataricus
Introduction
Genomic DNA is continuously subjected to a large variety
of lesions generated either by external agents or intrinsic
errors. To maintain the genome integrity, a rapid and accu-
rate detection of the damage is fundamental. If unrepaired
or misrepaired, DNA damage can cause genome instabil-
ity and/or cell death (Lindahl and Wood 1999; Nishino
and Morikawa 2002). The quality control of DNA depends
on different repair mechanisms, such as mismatch repair,
nucleotide excision repair, cross-link repair, base exci-
sion repair, and double-strand breaks repair. In most of
those pathways, nucleases play a crucial role in removing
the damaged or mismatched nucleotides (Ramadan et al
2002). One of the most harmful DNA lesions is the dou-
ble-strand break (DSB) indeed, if not correctly repaired;
it may result in chromosome loss or deletions, transloca-
tions, and genomic instability and affect negatively the
proliferation of normal cells, eventually causing cell death.
In eukaryotic cells the two major DSB repair pathways
are non-homologous end joining (NHEJ) and homologous
recombination (HR). In the NHEJ pathway the two ends of
the broken chromosome are ligated back together directly
in an error-prone process. On the contrary, HR is a high-
fidelity mechanism since it relies on homologous DNA
sequences generating error-free products (Niu et al 2010;
Longhese et al 2010). It has been suggested that in eukary-
otes, DSBs that take place in the G1 phase of the cell cycle
are most probably repaired via NHEJ, while those occur-
ring in the S/G2 phase are mainly processed via HR (Bern-
stein and Rothstein 2009; Chapman et al 2012). During
HR a core protein complex formed by Mre11-Rad50-Nbs1/
Mre11-Rad50-Xrs2 (human MRN and Saccharomyces
cerevisiae MRX, respectively) in conjunction with Ctp1/
CtIP (or Sae2), recognizes the lesion and removes a few
nucleotides to form an early intermediate of HR (Lengs-
feld et al 2007; Nicolette et al 2010; Mimitou and Syming-
ton 2008; Cejka et al 2010). The EXO1/Exo1 nuclease, the
BLM/Sgs1 helicase, and the DNA2/Dna2 nuclease play
a prominent role in HR by binding to late HR intermedi-
ates and generating 3′-ssDNA overhangs (Mimitou and
Communicated by L. Huang.
* Mariarosaria De Falco
mariarosaria.defalco@ibbr.cnr.it
* Mariarita De Felice
mariarita.defelice@ibbr.cnr.it
1
Institute of Biosciences and Bioresources, Consiglio
Nazionale delle Ricerche, 80131 Naples, Italy
@Phil_Robichaud
@deepthiw
@JoseServera