Individual deletion of each of both eIF4A-gene copies only had a very mild effect, deletion of eIF4B and eIF4G1 lead to a significant loss in adhesion and pseudohyphenating properties (Figure S3). These results clearly indicate that these properties are not only dependent on eIF4Eactivity but also rely on other components of the eIF4F complex. Surprisingly, deletion of eIF4G2 had an opposite effect as we detected increased adhesive and pseudohyphenating properties of the knockout strain when compared to wt cells (Figure S3).DiscussionThis study shows that mutations in eIF4E and knockouts of components of the eIF4F complex influence adhesive properties of haploid yeast cells and the ability of diploid cells to undergo pseudohyphenation upon nitrogen starvation. Especially well studied here were mutants that affect eIF4E expression levels and activity. One of those mutations (E105Q) was localised in the cap-binding groove affecting its interaction with the cap structure of mRNAs. It is not known, if defects in this interaction affect the translation of all capped mRNAs to a similar extend or if the nucleotides following the cap further modulate this effect. A further electrostatic interaction which has been shown to stabilize interaction with capped mRNAs is due to positive charges on eIF4E interacting with the negative charges of the three phosphate residues which form the unusual link of 7mG to the second nucleotide at the 59-end of capped mRNAs (which is often also a G) [28]. We have created eIF4E mutants K114L (lysine 104 to leucine), R157L (arginine 157 to leucine) and K162L (lysine 162 to leucine) abolishing nearby positive charges which could interact electrostatically with phosphate residues. All three basic residues (especially R157) are among the most conserved amino acids of eIF4E from different eukaryotic species [30]. None of these mutants were lethal, but especially R157L has a strong slow growth and temperature-sensitive phenotype. All 3 mutants showed reduced adhesion, especially haploid R157L which did not adhere and showed no pseudohyphenation (results not shown). Surprisingly, eIF4E’s level and activity can be substantially reduced in yeast cells without having negative effects on growth under laboratory conditions as it is shown for our eIF4E temperature sensitive strains. Strong reductions in eIF4E level without major effects on overall translation have been recently shown for mammalian cells [31]. Nevertheless, our eIF4E ts-mutants have clearly lost adhesive and pseudohyphenation properties which might be of upmost importance for the 1407003 survival of yeast strains in a natural environment characterized by sudden changes in temperature, humidity and nutritional conditions and where yeasts have to compete with many other organisms for survival. A mutation in yeast eIF4E (W75A) which affects its interaction with p20 or a knockout strain of p20 do not show a notable decrease in these properties. This is opposed to previously published data describing loss of pseudohyphenation in a diploid homozygous Dp20 knockout strain [8]. We don’t have an explanation for these contradicting data. We conclude that the presence or absence of p20 is a less decisive factor for adhesive properties of yeast strains such as those examined in this work. This does not exclude that eIF4E-p20 interaction might modulate the translational rate of certain genes required for adhesive properties [32]. As shown in this paper, in the yeast S. cerevisiae cap.