Enzyme that catalyzes the hydrolysis of both DNA and RNA at the 5'-position of the phosphodiester bond. Endonucleolytic cleavage to nucleoside 3'-phosphates and 3'-phosphooligonucleotide end-products. Binds 1 Ca(2+) ion per subunit. Active at 37 degrees Celsius. Retains activity after heating at 100 degrees Celsius. Belongs to the thermonuclease family.