Human prothymosin alpha mutants were generated with the aid of random
mutagenesis and screened for their ability to inhibit yeast Saccharomy
ces cerevisiae cell growth. Conversion of Lys-87 to Glu resulted in an
inactivated prothymosin alpha mutant, which lost the ability of the m
ild-type protein to block yeast cell growth, We propose that prothymos
in alpha may possess a bipartite rather than monopartite nuclear local
ization signal, which includes Lys-87, and that the above mutation des
troys one part of the nuclear localization signal, thus preventing eff
icient nuclear uptake of prothymosin alpha.