A nucleic acid base for hole transportation in DNAs which does not cause oxidative decomposition; and an artificial DNA molecule which can realize effective hole transportation in DNAs while maintaining the double spiral structure of the DNAs. Provided are: a nucleic acid which contains a benzodeazaadenine derivative base represented by the general formula (I): ##STR00001## (wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 each independently represents hydrogen, amino, mono (lower alkyl) amino, di (lower alkyl) amino, hydroxy, lower alkoxy, halogeno, cyano, mercapto, lower alkylthio, or aryl; and R.sub.7 and R.sub.8 each independently represents hydrogen or a group bonded to phosphoric acid); and a polynucleotide comprising the nucleic acid.