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RusA proteins from the extreme thermophile Aquifex aeolicus and lactococcal phage r1t resolve Holliday junctions
Author(s) -
Sharples Gary J.,
Bolt Edward L.,
Lloyd Robert G.
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.02916.x
Subject(s) - aquifex aeolicus , holliday junction , biology , prophage , bacteriophage , genetics , dna , tn3 transposon , escherichia coli , genome , gene , homologous recombination , transposable element
Summary The RusA protein of Escherichia coli is a DNA structure‐specific endonuclease that resolves Holliday junction intermediates formed during DNA replication, recombination and repair by introducing symmetrically paired incisions 5 ′ to CC dinucleotides. It is encoded by the defective prophage DLP12, which raises the possibility that it may be of bacteriophage origin. We show that rusA ‐like sequences are indeed often associated with prophage sequences in the genomes of several bacterial species. They are also found in many bacteriophages, including Lactococcus lactis phage r1t. However, rusA is also present in the chromosome of the hyperthermophilic bacterium Aquifex aeolicus . In this case, there is no obvious association of rusA with prophage‐like sequences. Given the ancient lineage of Aquifex aeolicus , this observation provides the first indication that RusA may be of bacterial origin. The RusA proteins of A. aeolicus and bacteriophage r1t were purified and shown to resolve Holliday junctions. The r1t enzyme also promotes DNA repair in strains lacking the RuvABC resolvase. Both enzymes cleave junctions in a sequence‐dependent manner, but the A. aeolicus RusA shows a different sequence preference (3 ′ to TG) from the E. coli protein (5 ′ to CC), and the r1t RusA has relaxed sequence dependence, requiring only a single cytosine.