Structure of acridines and their effect on RNA synthesis in vitro.

1. Ledakrin (C-283), a 1-nitro-9-aminopropylacridine derivative, inhibits RNA synthesis in vitro if the complex with DNA is formed in the presence of thiol. 2. Using several analogues of Ledakrin, it has been found that the 1-nitro group is essential for enhancement of the inhibition by thiol; the length of 9-aminoalkyl side chain also plays a role in the reaction between DNA and the dye. 3. It is suggested that the low inhibitory effect of Ledakrin in the absence of thiol compounds is due to a steric hindrance between neighbouring 1-nitro and 9-aminoalkyl groups. This hypothesis has been confirmed by assaying inhibition of RNA synthesis by several analogues of Ledakrin.