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. Ubiquitous. Dual phosphorylation of Thr-250 and Thr-255 activates the kinase. Phosphorylation of Thr-385 activates the kinase. MAPK3/ERK1 is one of the kinases which activate MKNK1/MNK1. Phosphorylation by PAK2 leads to a reduced phosphorylation of EIF4G1. Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family.