Involved in peptide bond synthesis. Alleviates ribosome stalling that occurs when 3 or more consecutive Pro residues or the sequence PPG is present in a protein, possibly by augmenting the peptidyl transferase activity of the ribosome. Modification of Lys-34 is required for alleviation. Protein biosynthesis; polypeptide chain elongation. Is beta-lysylated on the epsilon-amino group of Lys-34 by the combined action of EpmA and EpmB, and then hydroxylated on the C5 position of the same residue by EpmC. Lysylation is critical for the stimulatory effect of EF-P on peptide-bond formation. The lysylation moiety would extend toward the peptidyltransferase center and stabilize the terminal 3-CCA end of the tRNA. The hydroxylation of the C5 position on Lys-34 would allow additional potential stabilizing hydrogen-bond interactions with the P-tRNA (Probable) (PubMed:20670890). Cells lacking EF-P display highly pleiotropic phenotypes similar to those lacking EmpA or EmpB. They exhibit reduced growth rates, and they display increased susceptibility to hypoosmotic conditions, antibiotics, and detergents and enhanced resistance to the compound S-nitrosoglutathione. The susceptibility phenotypes are largely explained by the enhanced membrane permeability of the efp mutant. Analysis of the membrane proteomes of wild-type and efp mutant strains reveals few changes, including the prominent overexpression of a single porin, KdgM (STM1131), in the efp mutant outer membrane. Belongs to the elongation factor P family.