Incorporation of 8-Azaguanine into Nucleic Acid of Tobacco Mosaic Virus

Abstract

THE guanine analogue, 5 amino-7-hydroxy-1-vtriazolo(d) pyrimidine (guanazolo; 8-azaguanine), delays or inhibits the development of infection in the case of several plant virus diseases¹. The activity of the compound is reversed by adenine, guanine and probably hypoxanthine, but not by several other naturally occurring purines. On current views of the action of antimetabolites, these facts would suggest that 8-azaguanine acts by blocking an enzyme system involved in the utilization of guanine and perhaps adenine by the virus. There is, however, the possibility that 8-azaguanine is sufficiently like guanine to be incorporated into the virus nucleic acid, replacing some of the guanine, but different enough to make a virus particle containing it incapable of further multiplication. With tobacco mosaic virus in inoculated tobacco leaves, 8-azaguanine causes a delay in the production of virus (measured by infectivity, by particle counts using electron microscopy, or by yield of extractable virus²). The results described here show that 8-azaguanine is incorporated into the nucleic acid of tobacco mosaic virus.