Giardia lamblia expresses a proteobacterial-like DnaK homolog

We identified a novel gene encoding molecular chaperone HSP70 in the amitoc hondriate parasite Giardia lamblia. The predicted protein is similar to bac terial DnaK and mitochondrial HSP70s. The gene is transcribed and translate d at a constant level during trophozoite growth and encystation. Alignment of the sequence with a data set of cytosolic, endoplasmic reticulum (ER). m itochondrial, and DnaK HSP70 homologs indicated that the sequence was extre mely divergent and contained insertions unique to giardial HSP70s. Phylogen etic analyses demonstrated that this sequence was distinct from the cytosol ic and ER forms and was most similar to proteobacterial and mitochondrial D naKs. However, a specific relationship with the alpha proteobacterial and m itochondrial sequences was not strongly supported by phylogenetic analyses of this data set, in contrast to similar analyses of cpn60. These data neit her confirm nor reject the possibility that this gene is a relic of seconda ry mitochondrial loss; they leave open the possibility that it was acquired in a separate endosymbiotic event.