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. 1996 Jun 28;271(26):15675-81.
doi: 10.1074/jbc.271.26.15675.

A major tyrosine-phosphorylated protein of Trypanosoma brucei is a nucleolar RNA-binding protein

A Das  1 , G C Peterson, S B Kanner, U Frevert, M Parsons
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A major tyrosine-phosphorylated protein of Trypanosoma brucei is a nucleolar RNA-binding protein

A Das et al. J Biol Chem. .
Free article

Abstract

We have previously identified a set of tyrosine-phosphorylated proteins with apparent molecular masses of 44-46 kDa as some of the major tyrosine phosphorylated species in the protozoan parasite Trypanosoma brucei. We now show that these molecules, herein named Nopp44/46, are localized in the nucleolus. Using monoclonal antibodies, we have isolated Nopp44/46 cDNA clones from expression libraries. Sequence analysis reveals that the predicted amino acid sequence of the molecule is composed of an N-terminal unique region, an internal acidic region, and C-terminal repeat region. Analysis of the cDNA clones and genomic Southern analysis indicated that Nopp44/46 belongs to a multigene family in which different gene copies are very similar but vary in the number of repeats. Interestingly, the repetitive amino acid sequence motif contains multiple RGG (Arg-Gly-Gly) boxes characteristic of RNA-binding proteins. In vitro binding experiments demonstrated that Nopp44/46 is indeed capable of binding nucleic acids. Competition experiments with different RNA homopolymers demonstrated that Nopp44/46 preferentially binds to poly(U). These studies suggest that Nopp44/46 may play a role in RNA metabolism in trypanosomes and raise the possibility that tyrosine phosphorylation may regulate the process.

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