Enzymes that catalyze the endonucleolytic cleavage of single-stranded regions of DNA or RNA molecules while leaving the double-stranded regions intact. They are particularly useful in the laboratory for producing "blunt-ended" DNA molecules from DNA with single-stranded ends and for sensitive GENETIC TECHNIQUES such as NUCLEASE PROTECTION ASSAYS that involve the detection of single-stranded DNA and RNA.

Synonyms: Single Strand Specific DNA and RNA Endonucleases, Single-Strand Specific DNA and RNA Endonucleases, EC 3.1.30.1