A second elF4E protein in Schizosaccharomyces pombe has distinct elF4G-binding properties

Abstract

The eukaryotic cap-binding proteins belonging to the elF4E family are generally involved in mediating the recruitment of ribosomes to capped mRNA. We described previously a cap-binding protein (now called elF4E1) in Schizosaccharomyces pombe that appears to have all of the usual structural and functional attributes of an elF4E. We have now characterised a new type of cap-binding protein (eIF4E2) from this organism, which at the amino acid sequence level, is 52% identical and 59% similar to elF4E1. elF42 is not essential in S.pombe but has some novel properties that may be related to a special function in the cell. The ratio of elF4E2:elF4E1 in the cell shifts in favour of elF4E2 at higher temperatures. Despite having all of the dorsal face amino acids that have so far been associated with elF4G binding to elF4E1, elF4E2 binds the elF4E-binding domain of S.pombe elF4G >102-times weaker than elF4E1 in vitro. The elF4E2 cap-binding affinity is in the typical micromolar range. The results suggest that elF4E2 is not active on the main pathway of translation initiation in fission yeast but might play a role in the adaptation strategy of this organism under specific growth conditions. Moreover, they provide insight into the molecular characteristics required for tight binding to elF4G.