GU253314 9650 1 410 HIV-1 packaging signal GU253314 9650 925 1781 Rev-responsive element (RRE) GU253314 9650 1795 1912 complementary polypurine tract (cPPT) GU253314 9650 1926 2549 pac GU253314 9650 5323 6075 self-inactivating 3' LTR