RNA is thought to have been the original genetic and catalytic molecule for life because it is capable of storing genetic information like DNA but is also capable of performing metabolism like proteins.Needless to say, RNA is not as good as either in the things that either specializes in, and as a result, the theory goes, this RNA life was out-competed by subsequent life that used its RNA to make proteins to do the metabolism for it, and then by yet more subsequent life that used those proteins to make its RNA into DNA as a much more stable information storage medium.

Of course, there is the suggestion that proteins themselves somehow stored information and made the first RNA, which I think is the other theory that you are referring to. This "chicken and egg" question was settled by the observation that RNA is capable of metabolism as well as information storage.