May play a role in the response to environmental stress and cytokines. Appears to regulate translation by phosphorylating EIF4E, thus increasing the affinity of this protein for the 7-methylguanosine-containing mRNA cap. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Phosphorylated and activated by the p38 kinases and kinases in the Erk pathway. Interacts with the C-terminal regions of EIF4G1 and EIF4G2. Also binds to dephosphorylated ERK1 and ERK2, and to the p38 kinases. Ubiquitously expressed in all tissues examined, with high levels in skeletal muscle. Dual phosphorylation of Thr-209 and Thr-214 activates the kinase. Phosphorylation of Thr-344 activates the kinase. MAPK3/ERK1 is one of the kinases which activate MKNK1/MNK1. Phosphorylation by PAK2 leads to a reduced phosphorylation of EIF4G1 (By similarity). Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family.