Interfering with once-per-cell-cycle regulation of DNA replication initiation generates genome instability through over-replication and has been linked to early stages of cancer development. Here, we engineered different systems in budding yeast to induce over-replication in G1 and investigated its characteristics and consequences within the same cell cycle. To study replisome composition, we immunopurified replisomes via a GFP-tag on the Psf2 subunit of the GINS complex from S phase in the presence and absence of hydroxyurea and after unscheduled replication initiation in G1.