The fission yeast ortholog of eIF3a subunit is not functional in Saccharomyces cerevisiae

The Schizosaccharomyces pombe eIF3a ortholog (SpeIF3a) was shown to be unable to substitute for S. cerevisiae eIF3a (SceIF3a) in its essential function in the initiation of translation. Overproduction of SpeIF3a altered the distribution of SceIF3a but formation of the endogenous eIF3 complex was not affected. SpeIF3a was found to be more tightly bound to S. cerevisiae ribosomes than SceIF3a and other eIF3 subunits (eIF3g, eIF3i, eIF3j). The host cells displayed aberrant morphology and altered chitin deposition. SpeIF3a probably competes with SceIF3a for binding to either ribosomes or yet to be identified substrates.