Required for the activation and stability of deoxyhypusine synthase DHSc. Required for cell growth and survival. Protein modification; eIF5A hypusination. Heterotetramer formed by a homodimer of the non-catalytic regulatory subunit DHSp and a homodimer of the catalytic subunit DHSc where DHSc appears to bind spermidine and DHSp appears to bind NAD(+). RNAi-mediated knockdown causes cell growth arrest followed by death, loss of DHSp expression and a failure to sustain infection in mice. Belongs to the deoxyhypusine synthase family. Lacks the conserved active site Lys, and therefore lacks catalytic activity.