Although there is an incomplete understanding of how RNA helicases are regulated, it is possible that they operate at different steps of the RNAi pathway or performing different roles [66]. Discussion As shown in several studies, RNA helicases are involved in a wide variety of processes, some of them being essential for survival, as demonstrated for the yeast putative RNA helicases, where their knockouts were lethal [32]. These results are essential for the correct annotation of the Giardia genome, since many of the helicases identified in this study were automatically annotated either as helicases without indicating any further information and others just as hypothetical

proteins (http://​www.​giardiadb.​org). The PLX-4720 research buy genome of a number of organisms contains a large number of putative helicases [34] and, as we found in this work, the relationship between the number of DEAD-box and DExH-box RNA helicases is conserved in Giardia as it is has been reported for other organisms (Table 1). Although Giardia is considered as an early-branching eukaryote and has a smaller and more compact genome [67], our findings regarding the type and number of RNA helicases in Giardia highlight the importance of these molecules in the biology of eukaryotic cells. Since only a few DExD/H-box RNA helicases have been characterized biochemically,

FDA approved Drug Library most of the reports assigning a putative function are based on the presence of the conserved and characteristic motifs that can define a putative RNA helicase and its family. Here we used the presence of those motifs for classification performing an in silico approach and then by manual identification of each motif. Then we confirmed and refined each motif at each position. Our results were in agreement with the phylogenetic tree obtained, because pentoxifylline SF2 helicases were grouped specifically according to their sequence conservation as well as with the conservation of their motifs. The particular finding within the Giardia Ski2 family regarding the internal duplication of the ORF GL50803_87022, having two helicases

and Sec63 domains, probably indicates that the origin of this protein was by a fusion event of two ancestral prokaryotic genes, as proposed for the RNA helicases from Entamoeba histolytica EhDExH1 and EhDExH10 [33] and other homologous proteins from phylogenetically distant species. Unfortunately, the significance of this duplication found only in two early-branching parasitic SU5402 concentration intestinal protozoa is still unknown. The DEAD-box protein family is present in many organisms, being the major RNA family of helicases, which seem to be involved in many, if not all, steps of RNA metabolism [68]. Although some DEAD-box helicases are closely related and have been described as paralogs [33], the comparison among amino acid sequences of all full-length sequences showed no paralogous DEAD-box helicases in Giardia because these proteins only share 14–29% identity and 24–43% similarity.