Protein that can both mediate the addition of adenosine 5'-monophosphate (AMP) to specific residues of target proteins (AMPylation), and the removal of the same modification from target proteins (de-AMPylation), depending on the context (By similarity). The side chain of Glu-274 determines which of the two opposing activities (AMPylase or de-AMPylase) will take place (By similarity). Adenylyltransferase that mediates the addition of adenosine 5'-monophosphate (AMP) to specific residues of target proteins (PubMed:27138431). In vivo target proteins include the heat-shock 70 family proteins hsp-1 and hsp-3 and the translation elongation factors eef-1A, eef-1G and eef-2 (PubMed:27138431). Can AMPylate core histone H3 in vitro (PubMed:27138431). Can also act as a phosphodiesterase by mediating removal of ATP (de-AMPylation) from target proteins (By similarity). Decreases susceptibility to P.aeruginosa-mediated killing and might therefore play a role in the innate immune response (PubMed:27138431). ATP + L-tyrosyl-[protein] = diphosphate + O-(5'-adenylyl)-L-tyrosyl-[protein] ATP + L-threonyl-[protein] = 3-O-(5'-adenylyl)-L-threonyl-[protein] + diphosphate 3-O-(5'-adenylyl)-L-threonyl-[protein] + H2O = AMP + H(+) + L-threonyl-[protein] The side chain of Glu-274 determines which of the two opposing activities (AMPylase or de-AMPylase) will take place. In response to endoplasmic reticulum stress, mediates de-AMPylase activity (By similarity). Adenylyltransferase activity is inhibited by the inhibitory helix present at the N-terminus: Glu-274 binds ATP and competes with ATP-binding at Arg-415, thereby preventing adenylyltransferase activity (By similarity). In unstressed cells, disengagement of Glu-274 promotes adenylyltransferase activity (By similarity). Activation dissociates ATP-binding from Glu-274, allowing ordered binding of the entire ATP moiety with the alpha-phosphate in an orientation that is productive for accepting an incoming target hydroxyl side chain (By similarity). Forms homodimers; homodimerization might be required for adenylyltransferase activity. Predominantly localized to the endoplasmic reticulum and to the nucleus. Ubiquitously expressed, with high expression in the germline. Expressed at all developmental stages, with high expression during embryogenesis. The fido domain mediates the adenylyltransferase activity. Belongs to the fic family.