Profilins are small ubiquitous proteins that regulate cytoplasmic actin dynamics. They also bind to several nuclear proteins but the significance of these interactions is unclear. Marcell Lederer, Brigitte Jockusch and Martin Rothkegel now identify a new profilin ligand in a yeast two-hybrid screen (see ). p42POP - a hitherto unknown Myb-related transcription factor - contains one functional tryptophan cluster motif in its DNA-binding domain, an acidic domain, nuclear import and export signals, a leucine zipper, and a proline cluster that mediates profilin binding. p42POP, which is widely expressed in mouse tissues, acts as a repressor of transcription in luciferase assays; this activity is altered by interaction with profilin. Profilin and p42POP coprecipitate in vitro and, more importantly, they interact in vivo in both the cytoplasmic and nuclear compartments. Further biochemical, cell biological and genetic analyses are now needed, suggest the authors, to determine exactly how profilin regulates gene transcription and, more generally, how microfilament dynamics are linked to signal transduction.
