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+). Optimum pH is 7.0-8.0. Interacts with CYS6/CYSB; this interaction inhibits nuclease activity of CAN2. Expressed in leaves, stems and siliques. By hydrogen peroxide and cold stress. Belongs to the thermonuclease family.