TRMA cells without thiamine exhibit a time-dependent decrease in RNA ribose synthesis via transketolase. There is a time-dependent decrease in de novo RNA ribose synthesis through the nonoxidative pathway in TRMA cells depleted of thiamine, and there is a compensatory increase in glucose oxidation and ribose synthesis though G6PDH. Over 7 days, the fraction of RNA ribose derived from the oxidative pathway under thiamine-depleted conditions is approximately twice that in thiamine-replete medium. WT cells did not exhibit significant change in pentose cycle carbon flow between glucose oxidation and nonoxidative ribose synthesis at any time point throughout our study. (Mean ± SD; n = 9) ^*P < .001.