An Extracellular Nuclease from Serratia marcescens

The specificity of an extracellular nuclease from Serratia marcescens was examined with both RNA and DNA as substrates. The enzyme was found to act in a predominantly endonucleolytic manner with less than 2% of the degradation products being mononucleotides. Both DNA and RNA were degraded to di-, tri-, and tetranucleotides terminating in 5'-phosphoryl ends. The enzyme had the unusual property of hydrolyzing both single-stranded and doublestranded DNA and RNA at similar rates. No base preference was exhibited at either the 5' or 3' end of the oligonucleotide fragments. When the S. marcescens nuclease was used in conjunction with venom phosphodiesterase, RNA and DNA were rapidly degraded to 5'-mononucleotides. The enzyme is thus potentially useful as a reagent for the study of polynucleotide structure and sequence.