sentences:  HIV Gag protein is encoded by the HIV "gag" gene, HXB2 nucleotides 790-2292.The HIV p17 matrix protein (MA) is a 17 kDa protein, of 132 amino acids, which comprises the N-terminus of the Gag polyprotein.It is responsible for targeting Gag polyprotein to the plasma membrane via interaction with PI(4,5)P2 through its highly basic region (HBR).