GTPase that plays an essential role in the late steps of ribosome biogenesis. GTPase point mutations (but not a deletion mutant) are suppressed by mild overexpression of RelA, probably due to increased levels of the stringent response mediator (p)ppGpp. 50S subunits assembled in the absence of Der are defective and unable to assemble into 70S ribosomes. GTPase activity is stimulated by YihI. Overexpression rescues an rrmJ deletion, stabilizing the 70S ribosome. Der and RrmJ are likely to share a mechanism to stabilize 50S ribosomal subunits at a very late stage of 50S subunit maturation possibly by interacting with 23S rRNA or 23S rRNA/r-protein complex. Vmax increases 35% in the presence of full-length YihI and 90% in the presence of YihI missing the first 45 residues. Associates with the 50S ribosomal subunit in the presence of GMPPNP, a non-hydrolysable GTP analog, and thus probably also in the presence of GTP, but not in the presence of GDP or in the absence of nucleotide. Interacts with YihI via the last 490 residues. The 2 G (guanine nucleotide-binding) domains are essential for activity and function cooperatively. The KH-like domain is required for ribosome recognition. Lethality. In a depletion experiment cells grow normally for 4 hours, at which time there is no detectable protein left. After 4 hours cell growth decreases rapidly, the amount of 50S ribosomal subunit decreases, rRNA precursors accumulate. A 40S ribosomal subunit is detected which is missing proteins L9 and L18 and has slightly reduced amounts of L2 and L6 compared to wild-type ribosomes. Belongs to the TRAFAC class TrmE-Era-EngA-EngB-Septin-like GTPase superfamily. EngA (Der) GTPase family.