Regulation of a transmembrane protein gene family by the small RNA-binding proteins TbUBP1 and TbUBP2.

The loci Tb927.3.4070, 927.3.4080, Tb927.3.4090, 927.3.4100 and 927.3.4110 of Trypanosoma brucei encode five similar proteins with 13-14 transmembrane domains. Corresponding mRNAs are more abundant in bloodstream-form trypanosomes than in procyclics. The 4070, 4090 and 4110 genes have almost identical 3'-intergenic regions and the predicted proteins share a short C-terminal extension; a reporter mRNA with the 4110 3'-untranslated region was more abundant in bloodstream forms than procyclic forms. The 3'-untranslated regions for 4080 and 4100 are different, and that of 4080 gave procyclic-specific reporter expression. TbUBP1 and 2 are proteins with low-specificity RNA-binding activity. Over-expression of TbUBP2 in bloodstream forms increased the overall abundance of mRNA encoding the transmembrane proteins, whereas TbUBP1 and 2 RNA interference decreased it. RNAi targeting TbUBP1 and 2 in bloodstream forms decreased mRNA with a 4110 3'-untranslated region, but increased it for 4080. Thus TbUBP and TbUBP2 may accentuate developmental regulation of the Tb927.3.4070-927.3.4110 mRNAs.