Barrier-to-autointegration factor (BAF) is a double-stranded DNA (dsDNA)-binding protein crucial for retroviral DNA integration. It is also known to have important cellular roles in nematodes, flies and frogs. Now Tokuko Haraguchi and colleagues (p. 1959) shed light on its role in the human cell cycle. The researchers closely examined its localisation in various cell lines and were intrigued by the different patterns of localisation in immortal cell lines (where it tends to be found in the cytoplasm) and in mortal cell lines (where, in young cells at least, it localises to the nucleus). When they examined the immortal cells in more detail, they found that BAF depletion delays the progression of cells through S phase. But by what mechanism? The authors discuss several possibilities, including gene regulation or an influence on chromatin structure. However, since they also observe that BAF depletion causes the mislocalisation of lamin A - a component of the nuclear lamina - BAF could instead affect S-phase progression indirectly by stabilising this.