Inhibition by tryptophan of nucleolar RNA synthesis in salivary gland nuclei of Chironomus thummi.

Tryptophan, but not glutamine and lysine, inhibits the incorporation of 3H-uridine into nucleoli of explanted salivary glands by about 60%. In isolated nuclei also, the nucleolar incorporation of 3H-uridine triphosphate is reduced to about 50% by tryptophan. It is concluded that tryptophan acts directly at the nuclear level and the possible mechanisms.