Identification and molecular characterization of Mnk1b, a splice variant of human MAP kinase-interacting kinase Mnk1

Exp Cell Res. 2004 Oct 1;299(2):343-55. doi: 10.1016/j.yexcr.2004.06.006.


In this paper, we report the identification and molecular characterization of a splice variant of human Mnk1 which has been named as Mnk1b. Human Mnk1b mRNA is homologous to human Mnk1 mRNA but lacking a region corresponding to exon 19, which causes a change in the reading frame generating a stop codon. The resulting protein lacks the last 89 amino acids at the C-terminal region that are replaced by 12 amino acids with an entirely new sequence. The C-terminal end in Mnk1 corresponds to the extracellular signal-regulated kinase (ERK1/2) binding site. Although Mnk1b lacks this domain and, consequently, is not phosphorylated by ERK1/2, it is able, however, to phosphorylate eIF4E in vitro and in vivo in a mitogen-activated protein kinases-independent manner. This result suggests that Mnk1b may play a key role in regulating protein translation in the absence of stimuli. Interestingly, a significant population of cells shows Mnk1b within the nucleus whereas Mnk1 is always detected in the cytoplasm. This fact may be explained because Mnk1b maintains the nuclear localization signal (NLS) but lacks the nuclear export sequence (NES).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing*
  • Amino Acid Sequence
  • Binding Sites
  • Cell Nucleus
  • Eukaryotic Initiation Factor-4E / metabolism*
  • Genetic Variation / genetics*
  • Humans
  • Intracellular Signaling Peptides and Proteins
  • Mitogen-Activated Protein Kinase 1 / metabolism*
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases / metabolism*
  • Molecular Sequence Data
  • Phosphorylation
  • Protein Isoforms
  • Protein Serine-Threonine Kinases / genetics*
  • Protein Serine-Threonine Kinases / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Homology, Amino Acid


  • Eukaryotic Initiation Factor-4E
  • Intracellular Signaling Peptides and Proteins
  • Protein Isoforms
  • MKNK2 protein, human
  • Protein Serine-Threonine Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases