1. It must be able to store any random sequence of symbols belonging to a certain set (e.g. any possible sequence of bases in the case of nucleic acids).
2. There must be a way to make identical copies of it (e.g. nucleic acid replication).
(the previous 2 properties are true both for its own genetic material and for a foreign virus that does not have any use for a living being)
3. There must be a way to use the stored sequence of symbols to direct some process that is useful for a living being.
(for nucleic acids, the better known useful processes are protein synthesis and the synthesis of certain kinds of useful by itself RNA, but there are also some other poorly understood functions of most of the "junk" DNA)
