0 9 Infection infection NN 10 13 and and CC 14 25 replication replication NN 26 28 of of IN 29 33 Tat- tat- Tat- 34 39 human human JJ 40 56 immunodeficiency immunodeficiency NN 57 64 viruses virus NNS 64 65 : : : 66 73 genetic genetic JJ 74 82 analyses analysis NNS 83 85 of of IN 86 89 LTR LTR NNP 90 93 and and CC 94 97 tat tat NN 98 107 mutations mutation NNS 108 110 in in IN 111 118 primary primary JJ 119 122 and and CC 123 132 long-term long-term JJ 133 138 human human JJ 139 147 lymphoid lymphoid JJ 148 153 cells cell NNS 153 154 . . . 156 159 Tat Tat NNP 160 162 is be VBZ 163 165 an an DT 166 175 essential essential JJ 176 186 regulatory regulatory JJ 187 194 protein protein NN 195 198 for for IN 199 202 the the DT 203 214 replication replication NN 215 217 of of IN 218 223 human human JJ 224 240 immunodeficiency immunodeficiency NN 241 246 virus virus NN 247 248 ( ( ( 248 251 HIV HIV NNP 251 252 ) ) ) 252 253 . . . 254 263 Mutations mutation NNS 264 266 in in IN 267 270 the the DT 271 274 tat tat NN 275 279 gene gene NN 280 284 have have VBP 285 289 been be VBN 290 295 shown show VBN 296 298 to to TO 299 304 block block VB 305 308 HIV HIV NNP 309 320 replication replication NN 321 323 in in IN 324 329 human human JJ 330 331 T t NN 332 337 cells cell NNS 337 338 . . . 339 346 Several several JJ 347 354 studies study NNS 355 359 have have VBP 360 371 established establish VBN 372 376 that that IN 377 380 Tat Tat NNP 381 389 releases release VBZ 390 392 an an DT 393 403 elongation elongation NN 404 409 block block NN 410 412 to to TO 413 416 the the DT 417 430 transcription transcription NN 431 433 of of IN 434 437 HIV HIV NNP 438 442 long long JJ 443 451 terminal terminal JJ 452 458 repeat repeat NN 459 460 ( ( ( 460 463 LTR LTR NNP 463 464 ) ) ) 464 465 ; ; : 466 473 however however RB 473 474 , , , 475 477 it it PRP 478 480 is be VBZ 481 484 not not RB 485 490 known know VBN 491 498 whether whether IN 499 503 this this DT 504 513 mechanism mechanism NN 514 519 alone alone RB 520 522 is be VBZ 523 533 sufficient sufficient JJ 534 536 to to TO 537 544 explain explain VB 545 548 the the DT 549 554 block block NN 555 557 to to TO 558 561 HIV HIV NNP 562 573 replication replication NN 574 576 in in IN 577 582 human human JJ 583 584 T t NN 585 590 cells cell NNS 591 595 when when WRB 596 599 Tat Tat NNP 600 602 is be VBZ 603 609 absent absent JJ 609 610 . . . 611 613 It it PRP 614 616 is be VBZ 617 625 possible possible JJ 626 630 that that IN 631 634 Tat Tat NNP 635 637 is be VBZ 638 642 also also RB 643 649 needed need VBN 650 653 for for IN 654 659 other other JJ 660 669 functions function NNS 670 676 during during IN 677 680 HIV HIV NNP 681 692 replication replication NN 692 693 . . . 694 696 To to TO 697 701 test test VB 702 707 these these DT 708 718 hypotheses hypothesis NNS 718 719 , , , 720 722 we we PRP 723 730 studied study VBD 731 738 several several JJ 739 742 tat tat NN 743 750 mutants mutant NNS 750 751 , , , 752 761 including include VBG 762 765 two two CD 766 770 stop stop NN 771 776 codon codon NN 777 784 mutants mutant NNS 785 788 and and CC 789 792 one one CD 793 801 deletion deletion NN 802 808 mutant mutant NN 809 814 using use VBG 815 836 replication-competent replication-competent JJ 837 842 HIV-1 HIV-1 NNP 843 853 constructs construct NNS 854 862 carrying carry VBG 863 872 wild-type wild-type JJ 873 875 or or CC 876 882 mutant mutant JJ 883 887 LTRs ltr NNS 888 892 with with IN 893 906 modifications modification NNS 907 909 in in IN 910 913 the the DT 914 922 NF-kappa NF-kappa NNP 923 924 B B NNP 925 931 and/or and/or CC 932 935 Sp1 sp1 NN 936 943 binding binding NN 944 949 sites site NNS 949 950 . . . 951 953 In in IN 954 958 this this DT 959 964 study study NN 964 965 , , , 966 968 we we PRP 969 973 show show VBP 974 978 that that IN 979 983 Tat- tat- Tat- 984 989 HIV-1 HIV-1 NNP 990 994 with with IN 995 1004 wild-type wild-type JJ 1005 1009 LTRs ltr NNS 1010 1013 can can MD 1014 1023 replicate replicate VB 1024 1026 in in IN 1027 1031 HeLa HeLa NNP 1032 1037 cells cell NNS 1037 1038 , , , 1039 1042 and and CC 1043 1046 the the DT 1047 1052 virus virus NN 1053 1061 produced produce VBN 1062 1066 from from IN 1067 1071 HeLa HeLa NNP 1072 1077 cells cell NNS 1078 1081 can can MD 1082 1088 infect infect VB 1089 1096 primary primary JJ 1097 1107 peripheral peripheral JJ 1108 1113 blood blood NN 1114 1125 lymphocytes lymphocyte NNS 1126 1129 and and CC 1130 1141 macrophages macrophage NNS 1141 1142 . . . 1143 1145 It it PRP 1146 1149 was be VBD 1150 1155 found find VBN 1156 1160 that that IN 1161 1164 the the DT 1165 1176 propagation propagation NN 1177 1179 of of IN 1180 1183 the the DT 1184 1187 Tat Tat NNP 1188 1195 mutants mutant NNS 1196 1206 containing contain VBG 1207 1216 wild-type wild-type JJ 1217 1221 LTRs ltr NNS 1222 1225 was be VBD 1226 1230 less less RBR 1231 1240 efficient efficient JJ 1241 1245 than than IN 1246 1250 that that DT 1251 1253 of of IN 1254 1257 the the DT 1258 1270 LTR-modified ltr-modified JJ 1271 1274 Tat Tat NNP 1275 1282 mutants mutant NNS 1282 1283 . . . 1284 1289 Large large JJ 1290 1297 amounts amount NNS 1298 1300 of of IN 1301 1306 viral viral JJ 1307 1310 RNA RNA NNP 1311 1314 and and CC 1315 1324 particles particle NNS 1325 1329 were be VBD 1330 1341 synthesized synthesize VBN 1342 1344 in in IN 1345 1355 infections infection NNS 1356 1367 established establish VBN 1368 1373 using use VBG 1374 1377 the the DT 1378 1381 tat tat NN 1382 1389 mutants mutant NNS 1390 1394 that that WDT 1395 1402 contain contain VBP 1403 1411 modified modify VBN 1412 1416 LTRs ltr NNS 1416 1417 . . . 1418 1425 However however RB 1425 1426 , , , 1427 1431 this this DT 1432 1441 efficient efficient JJ 1442 1453 propagation propagation NN 1454 1456 of of IN 1457 1460 the the DT 1461 1473 LTR-modified ltr-modified JJ 1474 1477 tat tat NN 1478 1485 mutants mutant NNS 1486 1489 was be VBD 1490 1500 restricted restricted JJ 1501 1503 to to TO 1504 1508 some some DT 1509 1517 lymphoid lymphoid JJ 1518 1522 cell cell NN 1523 1528 lines line NNS 1529 1533 that that WDT 1534 1538 have have VBP 1539 1543 been be VBN 1544 1555 transformed transform VBN 1556 1560 with with IN 1561 1566 other other JJ 1567 1574 viruses virus NNS 1574 1575 . . . 1576 1580 Thus thus RB 1580 1581 , , , 1582 1589 despite despite IN 1590 1593 its its PRP$ 1594 1603 essential essential JJ 1604 1608 role role NN 1609 1612 for for IN 1613 1622 releasing release VBG 1623 1625 an an DT 1626 1636 elongation elongation NN 1637 1642 block block NN 1642 1643 , , , 1644 1647 Tat Tat NNP 1648 1650 is be VBZ 1651 1654 not not RB 1655 1664 otherwise otherwise RB 1665 1675 absolutely absolutely RB 1676 1684 required require VBN 1685 1688 for for IN 1689 1698 synthesis synthesis NN 1699 1701 of of IN 1702 1713 full-length full-length JJ 1714 1717 HIV HIV NNP 1718 1729 transcripts transcript NNS 1730 1733 and and CC 1734 1742 assembly assembly NN 1743 1745 of of IN 1746 1751 virus virus NN 1752 1761 particles particle NNS 1761 1762 . . . 1763 1769 Direct direct JJ 1770 1780 sequencing sequencing NN 1781 1783 of of IN 1784 1787 the the DT 1788 1793 viral viral JJ 1794 1801 genomes genome NNS 1802 1805 and and CC 1806 1817 reinfection reinfection NN 1818 1826 kinetics kinetic NNS 1827 1833 showed show VBD 1834 1836 no no DT 1837 1845 evidence evidence NN 1846 1848 of of IN 1849 1858 wild-type wild-type JJ 1859 1868 reversion reversion NN 1869 1873 even even RB 1874 1879 after after IN 1880 1889 prolonged prolonged JJ 1890 1899 infection infection NN 1900 1904 with with IN 1905 1908 the the DT 1909 1913 Tat- tat- JJ 1914 1919 virus virus NN 1919 1920 . . . 1921 1924 The the DT 1925 1937 implications implication NNS 1938 1941 for for IN 1942 1944 in in FW 1945 1949 vivo vivo FW 1950 1955 HIV-1 HIV-1 NNP 1956 1967 replication replication NN 1968 1971 and and CC 1972 1981 potential potential JJ 1982 1993 application application NN 1994 1996 of of IN 1997 2001 this this DT 2002 2008 system system NN 2009 2011 to to TO 2012 2015 the the DT 2016 2021 study study NN 2022 2024 of of IN 2025 2036 alternative alternative JJ 2037 2040 Tat Tat NNP 2041 2049 function function NN 2050 2053 are be VBP 2054 2063 discussed discuss VBN 2063 2064 . . .