This protein, the third in the GAG polyprotein coats the RNA genome of the virus. It binds to the packaging signal of the RNA and helps deliver the RNA to the virus particle as it assembles. The packaging signal consists of three hairpins in the RNA. The protein is basis and binds single stand nucleic acids. It coats the RNA and protects it from nucleases. This protein also helps in the annealing of the lys tRNA primer, the melting of secondary structure in the RNA. It has two zinc fingers which are needed to bind to the RNA packaging signal

For further information see: Alan Frankel and John A. T. Young, HIV-1: Fifteen proteins and an RNA Annual Review of Biochemistry 67: 1-25, 1998