YchF, a universally conserved protein, hitherto thought to be a GTPase, was shown to be an ATPase based on structural and biochemical studies on hOLA1, a human ortholog of YchF. However, the cellular role of YchF is unclear. Based on the presence of a RNA binding domain in this protein and significant homology to ribosome binding Obg family GTPases, we examined its ability to associate with the ribosome. Here, we show that Escherichia coli YchF binds the 50S and 70S ribosomal particles in a nucleotide independent manner and it hydrolyzes ATP utilizing a potassium dependent mechanism. A potassium mediated acceleration of hydrolysis activity was thus far known for a few GTPases. Like these, YchF too conserves the structural features required for K+ coordination, making it a unique ribosome binding ATPase utilizing a similar mechanism. Furthermore, we show that Lys78 is an important determinant of the potassium dependent ATPase activity. (C) 2011 Elsevier Inc. All rights reserved.