Enzyme that catalyzes the hydrolysis of both DNA and RNA at the 5' position of the phosphodiester bond. Possesses activity toward the single-stranded DNA, double-stranded DNA and RNA. May be involved in genomic DNA degradation during programmed cell death. Binds 1 Ca(2+) ion per subunit. Inhibited by Zn(2+). Belongs to the thermonuclease family.