8-Azaguanine inhibits growth in a variety of living

systems. The analog is incorporated into bacterial, viral, and mammalian RNA, replacing up to 5 % of the guanine residues (9). In B. cereus Smith and Matthews (21) found that 40 % of total RNA guanine can be replaced. Using the same organism, Mandel and Markham (14) showed that the analog appeared primarily in short-chain RNA, and, more recently, Levin (10) demonstrated that most of this 8-azaguanine is incorporated into sRNA. This paper reports studies of some of the molecular events preceding azaguanine-induced growth inhibition in a human cell line maintained in suspension culture. Such a system is ideal for the evaluation of cellular DNA, RNA, and protein synthesis, as well as for the study of azaguanine distribution in the various species of RNA. The concentration of inhibitor can easily be adjusted to produce any desired growth effect.