This is the most characterized fragment of the HIV transactivator protein (TAT). This arginine-rich TAT peptide penetrates plasma membrane directly, but not through endocytosis.
Ref: Wang, H. et al. J. Clin. Invest. 109, 1463 (2002); Ziegler et al. Biochem. 44, 138 (2005); Wender, PA. et al. Proc. Natl. Acad. Sci. USA 97, 13003 (2000).