Rpg1p, the subunit of the Saccharomyces cerevisiae eIF3 core complex, is a microtubule-interacting protein

The essential gene RPG1/TIF32 of Saccharomyces cerevisiae encodes the 110-kDa subunit of the translation initiation factor 3 (eIF3) core complex. In this study, the Rpg1p-specific monoclonal antibody PK1/1 was used to analyse the cellular distribution of Rpg1p by epifluorescence and confocal laser scanning microscopy (CLSM). In budded cells, a portion of Rpg1p was obviously co-localised with microtubules. In addition, CLSM revealed an accumulation of Rpg1p in a patch at the very end of cytoplasmic microtubules reaching the bud tip. A punctate fluorescence pattern was typical for separated unbudded cells. Distribution of Rpg1p was confirmed using a strain expressing exclusively a hemaglutinin-tagged version of Rpg1p. In nocodazole-treated cells, the pattern of the PK1/1 staining was disturbed. No staining was observed in Rpg1p-depleted cells. In vitro experiments revealed that Rpg1p was specifically co-immunoprecipitated with alpha-tubulin from the yeast cell free extract and this observation was further supported by showing that Rpg1p co-sedimented with hog brain microtubules. We conclude that Rpg1p is a microtubule-interacting protein that indicates an interesting connection between the translation initiation machinery and cytoskeleton in yeast Saccharomyces cerevisiae.