Targeting of cytoskeletal proteins to the flagellum of Trypanosoma brucei

The eukaryotic flagellum represents one of the most complex macromolecular structures found in any organism and contains more than 250 proteins. Due t o the relative ease of genetic manipulation the flagellum of Trypanosoma br ucei has emerged as an accessible model system to study the morphogenesis a nd dynamics of this organelle. We have recently started to characterise the mechanisms by which components of the cytoskeletal fraction of the flagell um, such as the axoneme, the paraflagellar rod and the flagellar attachment zone, are targeted by proteins synthesised in the cytoplasm and assembled. Here, we present the identification of a novel actin-related protein as a component of the axoneme. We show that this protein shares the tripeptid mo th histidine-leucine-alanine (HLA) with one of the major proteins of the pa raflagellar rod, PFRA, Building on previous work from this lab which showed that a deletion comprising this motif abolished targeting of PFRA to the f lagellum we demonstrate in this study that the deletion of the tripeptid mo th is sufficient to achieve mistargeting both of the PFRA and the actin-rel ated protein. We propose that this motif represents an essential part of a flagellar targeting machinery in trypanosomes and possibly in other flagell ated organisms.