Effect of beta-indoleacetic acid on RNA and protein synthesis in Escherichia coli.

The effect of different concentrations of beta-indoleacetic acid (IAA) on RNA and protein synthesis and the stability of associations of E. coli ribosomes at 3 mM Mg2+ was investigated. IAA in a concentration of 100 microgram/ml had a slight stimulatory effect on the incorporation of [14C]leucine into proteins and stimulated the incorporation of [14C]uracil into the RNA of intact cells more noticeably. In the presence of 2500 microgram/ml of the auxin RNA synthesis was inhibited by 65% and protein synthesis by 40-50% as compared to the control. In a cell-free system containing poly(U) IAA in concentrations of 10-100 microgram/ml increased polyphenylalanine synthesis by an average of 30%, while at high concentrations IAA noticeably inhibited its synthesis. It was found that the proportion of stable ribosomes in lysates obtained from cells incubated with IAA in concentrations of 250 and 1000 microgram/ml decreased to 18 and 3%. It is suggested that the inhibition of protein synthesis in E. coli by IAA is due to inhibition of the initiation of translation.