Prothymosin alpha is an acidic nuclear protein that is expressed at high levels in a wide variety of cell types. Accumulating data correlate prothymosin expression with alterations in the proliferative state of cells. Some data indicates that prothymosin may actually be necessary, if not sufficient, for proliferation, and that prothymosin may function in a c-myc associated pathway. Prothymosin is highly conserved through evolution suggesting a key function, however, that function remains unknown.