Discovery of the nucleolar targeting signal.

The discovery of the signal peptides that direct proteins to localize at the nucleolus is described here. The nucleolar targeting signal termed the NOS consists of clustered basic amino acids organized such that a portion also functions as the nuclear transporting signal. Although a NOS has been identified within the regulatory genes of human retroviruses, HTLV-I and HIV-I, signals of similar function in cellular proteins--such as heat shock proteins--may be induced through the configurational change of protein structure by heat or stress.