We performed mass-spectrometry analysis of proteins co-purifying with Whi5, a predicted repressor of the MBF transcriptional complex. Whi5 was tagged with GFP at its C-terminal end and expressed from its endogenous promoter at its chromosomal locus. Whi5-GFP was immunoprecipitated from cells growing in MM and after 16 hours in MM-N, and co-purifying proteins were analysed by mass-spectrometry. An untagged wild-type strain was used as a control.