Formally recognized approximately 40 years ago, Archaea is still the least studied of the three domains of life. Euryarchaeota and Crenarchaeota are the two major phyla of Archaea, and the most well understood, particularly because of the existence of genetic techniques that allow for their study. An important crenarchaeal model organism is Sulfolobus acidocaldarius, a motile aerobic thermoacidophile first isolated from terrestrial volcanic environments that thrives at around 75°C and pH 3. The archaellum – an organelle functionally similar to the bacterial flagellum, but structurally and genetically different – is responsible for the locomotion of motile archaeal species. In recent years it has been found that the expression of this organelle depends on environmental factors, and starvation in particular is associated with archaella induction in S. acidocaldarius. The signal transduction of nutrient depletion to archaella expression is not fully understood, but recently some key players of the archaellum regulatory network have been uncovered. Specifically, ArnA and ArnB were found to be negative regulators of archaella expression. Moreover, both proteins were found to be phosphorylated, which points at the existence of a multi-level regulatory system. Saci_1563 is a protein conserved in several Crenarchaeota species that was found to be co-purified with ArnA. This protein is a putative GTP-binding protein, a class of proteins implicated in the regulation of several biological phenomena and in cell signalling. It is thus plausible that Saci_1563, by acting as a molecular switch, is implicated in the fine tuning of archaella expression in response to specific signals. In this study we assessed the biological role of Saci_1563 and its biochemical characterization. Protocols for the heterologous purification of this protein in Escherichia coli and for the purification of over-expressed protein in S. acidocaldarius were optimised. The purified protein was then subject to phosphate release assays to test for its GTP-binding ability. The impact of saci_1563 deletion on S. acidocaldarius motility was tested, and the influence of starvation on saci_1563 expression was determined. Moreover, we analysed the effect of saci_1563 deletion on the expression of proteins belonging to the archaellum regulatory network and to the archaellum operon. The results reported in this thesis are far from conclusive. A role for Saci_1563 in archaella regulation cannot be excluded, but other venues of research regarding this protein are suggested.