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# Old_exonuclease
## Description
The OLD proteins are a family of nucleases present in bacteria, archaea, and viruses :ref{doi=10.1093/nar/gkz703}. The OLD protein found in the P2 *E.coli* prophage is the best characterized one. The protein is an exonuclease that digests dsDNA in the 5' to 3' direction :ref{doi=10.1128/jb.177.3.497-501.1995}. It also has nuclease activity against single stranded DNA and RNA :ref{doi=10.1128/jb.177.3.497-501.1995}. It's been shown to protect against phage lambda :ref{doi=10.1128/jb.177.3.497-501.1995}, and when cloned with the P2 Tin accesory gene, it was shown to protect against other *E. coli* phages :ref{doi=2022 10.1016/j.chom.2022.02.018}. The protein also contains an ATPase domain that affects nuclease activity :ref{doi=10.1128/jb.177.3.497-501.1995}. Inhibition of the RecBCD complex activates the OLD nuclease :ref{doi=10.1016/j.mib.2023.102325}. OLD proteins are divided into two classes based on amino acid sequence conservation and gene neighborhood :ref{doi=10.1093/nar/gkz703}. The P2 associated protein belongs to class 2 :ref{doi=10.1093/nar/gkz703}.
The OLD proteins are a family of nucleases present in bacteria, archaea, and viruses :ref{doi=10.1093/nar/gkz703}. The OLD protein found in the P2 *E.coli* prophage is the best characterized one. The protein is an exonuclease that digests dsDNA in the 5' to 3' direction :ref{doi=10.1128/jb.177.3.497-501.1995}. It also has nuclease activity against single stranded DNA and RNA :ref{doi=10.1128/jb.177.3.497-501.1995}. It's been shown to protect against phage lambda :ref{doi=10.1128/jb.177.3.497-501.1995}, and when cloned with the P2 Tin accesory gene, it was shown to protect against other *E. coli* phages :ref{doi=10.1016/j.chom.2022.02.018}. The protein also contains an ATPase domain that affects nuclease activity :ref{doi=10.1128/jb.177.3.497-501.1995}. Inhibition of the RecBCD complex activates the OLD nuclease :ref{doi=10.1016/j.mib.2023.102325}. OLD proteins are divided into two classes based on amino acid sequence conservation and gene neighborhood :ref{doi=10.1093/nar/gkz703}. The P2 associated protein belongs to class 2 :ref{doi=10.1093/nar/gkz703}.
## Molecular Mechanisms
The old_exonuclease is dsDNA exonuclease that digest in the 5' to 3' direction :ref{doi=10.1128/jb.177.3.497-501.1995}. To our knowledge, other aspects of the molecular mechanisms remain unknown.