Prokaryotes are unicellular organisms that lack organelles or other internal membrane-bound structures. They do not have a nucleus and lack histones (with a few exceptions). Genetic information in prokaryotic cells is carried on a single circular piece of DNA which is attached to the cell membrane and in direct contact with the cytoplasm. There is no enclosing membrane, as there is no true nucleus, but simply a concentration of DNA known as a nucleoid.
hence the ratio of DNA: histones in prokaryotes can be given as 1:0.