Trypanosomes Depend on Post-transcriptional Mechanisms to Regulate Gene Expression

The genome organization of trypanosomes, leishmanias, and related kinetoplastid organisms is highly unusual: Each RNA polymerase II promoter precedes multiple open reading frames, and the primary transcript is cut into individual mRNAs by 59 trans splicing and 39 polyadenylation [1]. Dedicated control of transcription at the level of individual mRNAs is therefore not possible. Nevertheless, mRNA levels are highly controlled: Although some gene sequences are represented by several hundred mRNAs, most mRNAs are present at just one or two copies per cell [2]. Constitutively high mRNA levels can be obtained by having many identical genes, but for most genes, more flexible control points are used: mRNA processing, export from the nucleus, translation, and mRNA decay. Kinetoplastid mRNAs are probably bound by multiple proteins possessing varying degrees of sequence specificity. The poly(A) tai