Angiogenin is endocytosed by subconfluent endothelial cells, translocated to the 
nucleus and accumulates in the nucleolus. It also localizes into the nucleolus 
of digitonin-permeabilized endothelial cells. The peptide RRRGL corresponding to 
residues 31-35 of human angiogenin specifically targets non-nuclear carrier 
proteins such as albumin, an anti-human nucleolus monoclonal antibody and R33A 
angiogenin to the nucleolus of permeabilized endothelial cells. Proteins 
conjugated with a "mutant" peptide, RRAGL, are not imported. Fluorescein 
isothiocyanate-conjugated RRRGL is also rapidly imported into the nucleus and 
localized to the nucleolus, whereas the "mutant" peptide is not. Residue R33 is 
essential for nuclear translocation and R31 and R32 appear to modulate this 
process. Thus, 31RRRGL35 is a nuclear localization signal responsible for the 
nucleolar targeting of human angiogenin.