Using a whole-cell proteome approach, we investigated the effect of the mug174+ gene deletion on the proteome during vegetative growth and G0/cellular quiescence in the fission yeast Schizosaccahromyces pombe. We revealed that (1) Mug174 ensured the protein expression from intron-containing genes during vegetative growth, and (2) the proteins involved in ribosome biogenesis were increased, whereas some of the G0 essential proteins were decreased in the absence of Mug174. The data from our proteome analyses indicated that Mug174 is essential for proper protein expression.