An RNA-dependent UMP-incorporating activity is associated with the small subunit of cytoplasmic ribosomes in bloodstream forms of Trypanosoma brucei.

Trypanosoma brucei cytoplasm contained a UMP-incorporating activity which was dependent upon the presence of endogenous RNA, stimulated by exogenous RNA and precipitable by ammonium sulphate. The activity cosedimented with ribosomes, and after ribosome dissociation using EDTA was mainly associated with the small (31S) subunit. Ribosome-associated activity was selective for UTP as a substrate and greatly stimulated by the presence of at least one other nucleoside triphosphate.