Lysine-87 is a functionally important residue in human prothymosin α

Human prothymosin a mutants were generated with the aid of random mutagenesis and screened for their ability to inhibit yeast Saccharomyces cerevisiae cell growth. Conversion of Lys-87 to Glu resulted in an inactivated prothymosin α mutant, which lost the ability of the wild-type protein to block yeast cell growth. We propose that prothymosin α may possess a bipartite rather than monopartite nuclear localization signal, which includes Lys-87, and that the above mutation destroys one part of the nuclear localization signal, thus preventing efficient nuclear uptake of prothymosin α.