Practice question

S1 nuclease is a zinc-dependent acidic endonuclease purified from the filamentous fungus Aspergillus oryzae. It exhibits high specificity for single-stranded nucleic acids, degrading unpaired DNA and RNA into 5'-mononucleotides while leaving fully base-paired duplexes largely intact under titrated conditions. Its activity requires zinc ions and low pH around 4.5. Molecular biologists utilize S1 nuclease to remove single-stranded overhangs after restriction digestion to create blunt ends, to cleave hairpin loops formed during second-strand cDNA synthesis, and to map transcription start sites and RNA-DNA hybrids.