1. U.S. Patent 4,206,243.
2. K. Ogata, S. Kinoshita, T. Tsunoda, and K. Aida, “Microbial Production of Nucleic Acid-Related Substance,” Wiley, New York.
3. Japanese Patent Application 5,320,494.
4. Japanese Patent Application 5,455,791.
5. German Offenlegungsschrift 3,136,940.