The enzymatic basis of processivity in λ exonuclease

Krithika Subramanian, Wiriya Rutvisuttinunt, Walter Scott, Richard S. Myers

Research output: Contribution to journalReview articlepeer-review

92 Scopus citations


λ Exonuclease is a highly processive 5��3� exonuclease that degrades double-stranded (ds)DNA. The single-stranded DNA produced by exonuclease is utilized by homologous pairing proteins to carry out homologous recombination. The extensive studies of biology, exonuclease enzymology and the availability of the X-ray crystallographic structure of exonuclease make it a suitable model to dissect the mechanisms of processivity. Exonuclease is a toroidal homotrimeric molecule and this quaternary structure is a recurring theme in proteins engaged in processive reactions in nucleic acid metabolism. We have identified residues in exonuclease involved in recognizing the 5�-phosphate at the ends of broken dsDNA. The preference of exonuclease for a phosphate moiety at 5� dsDNA ends has been established in previous studies; our results indicate that the low activity in the absence of the 5�-phosphate is due to the formation of inert enzyme-substrate complexes. By examining a exonuclease mutant impaired in 5�-phosphate recognition, the significance of catalytic efficiency in modulating the processivity of exonuclease has been elucidated. We propose a model in which processivity of exonuclease is expressed as the net result of competition between pathways that either induce forward translocation or promote reverse translocation and dissociation.

Original languageEnglish (US)
Pages (from-to)1585-1596
Number of pages12
JournalNucleic acids research
Issue number6
StatePublished - Mar 15 2003

ASJC Scopus subject areas

  • Genetics


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