Silkworm Nuclease-Its Nature and Promise

An endonuclease was purified from the digestive juice of silkworm larvae, B o m b y x mori. The enzyme hydrolyses both DNA and RNA endolytically with little base specificity, yielding diand trinucleotides terminating in 5’-phosphate. Polynucleotides terminated in 3’ -phosphate gave dinucleosidemonophosphates and trinucleosidediphosphates f rom 5’-end, diand trinucleotides from inside, a n d mononucleosidediphosphates, dinucleosidetriphosphates, and t r inuc leos ide te t raphosphates f rom 3’-end, respectively. Taking advantage of these peculiar nature of the nuclease, an oligonucleotide addition procedure was devised to sequence nucleic acids from the overlapping pattern of the fragments of digestion by the nuclease. Proven and potential usefulness of the silkworm endonuclease in the structural work on nucleic acids and specificity analysis of nucleolytic enzymes were discussed.