EFO1 (Establishment factor-like protein 1), also known as ESCO1 (establishment of cohesion 1 homolog1) or ESO1, is a member of the acetyltransferase family (GCN5 subfamily). It is a ubiquitously expressed nuclear protein that plays an important role in sister chromatid cohesion. At its C-terminus, EFO1 contains an H2C2 zinc finger motif and an acetyltransferase domain that exhibits acetyltransferase activity in vivo. Its N-terminus, containing two domains that are similar to ẟ- and β-type linker histone proteins, is essential for EFO1 association with chromosomes. EFO1 is responsible for coupling cohesion and DNA replication processes thereby ensuring proper pairing of sister chromatids. EFO1 is phosphorylated during mitosis and this may act to regulate EFO1 activity. Due to alternative splicing events, three EFO1 isoforms exist.