Regulation of Gene Expression in Leishmania Throughout a Complex Digenetic Life Cycle
Barbara Papadopoulou, Michaela Müller, Annie Rochette, François McNicoll, Carole Dumas and Conan Chow
from: Leishmania: After The Genome (Edited by: Peter J. Myler and Nicolas Fasel). Caister Academic Press, U.K. (2008)
In comparison to all other organisms, from Escherichia coli to man, Leishmania and related trypanosomatid protozoan parasites show unique features with respect to their regulation of gene expression in response to changes in their environment. The recent completion of the L. major and L. infantum genome projects indicates that protein-coding genes are organized as large polycistronic units in a head-to-head or tail-to-tail manner. RNA polymerase II transcribes long polycistronic messages in the absence of defined RNA pol II promoters. As the result of polycistronic transcription, mRNA synthesis requires posttranscriptional control, which involves 5' trans-splicing of a 39-nt capped leader RNA and 3' cleavage polyadenylation. Several examples in Leishmania support the notion that developmental regulation of mRNA levels is determined post-transcriptionally by sequences located in the 3'-untranslated regions (3'UTR) that usually control mRNA stability and translation. Posttranslational regulation is also associated with stage-specific gene expression. The lack of promoter elements for RNA pol II and the unusually long 3'UTR sequences provide the molecular basis for this type of control. Posttranscriptional controls at translational and posttranslational levels could play major roles in differentiation in Leishmania parasites. Stage-specific posttranscriptional regulation is complex and involves the coordination of different mechanisms that can be independently triggered by environmental signals inducing differentiation of promastigotes to amastigotes within mammalian macrophages read more ...