Signal-sequence-independent secretion of the staphylococcal nuclease in Mycobacterium smegmatis

Microbiology (Reading). 2002 Feb;148(Pt 2):529-536. doi: 10.1099/00221287-148-2-529.


Staphylococcus aureus nuclease is a small, secreted protein which has been successfully used as a reporter system to identify exported products in Lactococcus lactis. Here, biochemical evidence is provided that the nuclease is exported by Mycobacterium smegmatis in the presence, but also in the absence of a signal sequence, and thus probably independently of the Sec translocation pathway. This implies that the nuclease should not be used as a reporter system in mycobacteria for the identification of exported products, despite what has been reported previously in the literature. The nuclease can be extended to create hybrid proteins that remain compatible with its secretion, whereas some other shorter fusions are not tolerated. This suggests that correct folding is required for efficient export. Extensive mutational analysis did not identify a specific secretion pathway. This suggests that the nuclease may be exported by different redundant systems or that components of this alternative Sec pathway are essential for bacterial survival.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • DNA, Bacterial / genetics
  • Genes, Reporter
  • Micrococcal Nuclease / chemistry
  • Micrococcal Nuclease / genetics
  • Micrococcal Nuclease / metabolism*
  • Mycobacterium smegmatis / genetics*
  • Mycobacterium smegmatis / physiology
  • Protein Folding
  • Protein Sorting Signals / genetics
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism


  • DNA, Bacterial
  • Protein Sorting Signals
  • Recombinant Fusion Proteins
  • Micrococcal Nuclease