The initiation factor eIF4A is involved in the response to lithium stress in Saccharomyces cerevisiae.
A gene, TIF2, was identified as corresponding to the translation initiation factor eIF4A and when overexpressed it confers lithium tolerance in galactose medium to Saccharomyces cerevisiae. Incubation of yeast with 6 mm LiCl in galactose medium leads to inhibition of [(35)S]methionine incorporation. By polysome analysis we show that translation is inhibited by lithium at the initiation step, accumulating 80 S monosomes. We further show by immunoblot analysis that when cells are incubated with lithium eIF4A does not sediment with ribosomal subunits. Overexpression of TIF2 overcomes inhibition of protein synthesis and restores its sedimentation with the initiation complex. In vivo, eIF4A is induced by lithium stress. We have shown previously that lithium is highly toxic to yeast when grown in galactose medium mainly due to inhibition of phosphoglucomutase, an enzyme responsible for the entry of galactose into glycolysis. We show that conditions that revert inhibition of phosphoglucomutase also revert inhibition of protein synthesis. Interestingly, glucose starvation leads to loss of polysomes but not to dissociation of eIF4A from the preinitiation complexes. Overexpression of SIT4, a protein phosphatase related to the TOR kinase pathway, reverts inhibition of protein synthesis by lithium and association of eIF4A with the initiation complex.
Montero-Lomeli
Monica
M
Departamento de Bioquimica Médica, ICB-CCS, Universidade Federal do Rio de Janeiro, C.P. 68041, Rio de Janeiro, R.J. 21941-590, Brazil. montero@server.bioqmed.ufrj.br
Morais
Bruno L B
BL
Figueiredo
Daniela L
DL
Neto
Domingos C S
DC
Martins
João R P
JR
Masuda
Claudio A
CA
D015153:Blotting, Western; D002352:Carrier Proteins / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D039601:Eukaryotic Initiation Factor-4A; D005285:Fermentation / Q000187:drug effects; D005690:Galactose / Q000494:pharmacology; D015151:Immunoblotting; D008094:Lithium / Q000494:pharmacology*; D018021:Lithium Chloride / Q000494:pharmacology; D051958:Nuclear Receptor Coactivator 2; D010448:Peptide Initiation Factors / Q000502:physiology*; D010733:Phosphoglucomutase / Q000037:antagonists & inhibitors; D010749:Phosphoprotein Phosphatases; D011132:Polyribosomes / Q000378:metabolism; D011485:Protein Binding; D054648:Protein Phosphatase 2; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000502:physiology*
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D051958:Nuclear Receptor Coactivator 2; D010448:Peptide Initiation Factors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D013912:Threonine; D012694:Serine; D008094:Lithium; D039601:Eukaryotic Initiation Factor-4A; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae; D010733:Phosphoglucomutase; D018021:Lithium Chloride; D005690:Galactose