0 3 The the DT 4 7 tax tax NN 8 15 protein protein NN 16 18 of of IN 19 24 human human JJ 25 31 T-cell t-cell NN 32 40 leukemia leukemia NN 41 46 virus virus NN 47 51 type type NN 52 53 1 1 CD 54 62 mediates mediate VBZ 63 66 the the DT 67 82 transactivation transactivation NN 83 85 of of IN 86 89 the the DT 90 112 c-sis/platelet-derived c-sis/platelet-derived JJ 113 119 growth growth NN 120 128 factor-B factor-b NN 129 137 promoter promoter NN 138 145 through through IN 146 158 interactions interaction NNS 159 163 with with IN 164 167 the the DT 168 172 zinc zinc NN 173 179 finger finger NN 180 193 transcription transcription NN 194 201 factors factor NNS 202 205 Sp1 sp1 NN 206 209 and and CC 210 222 NGFI-A/Egr-1 ngfi-a/egr-1 NN 222 223 . . . 225 240 Transcriptional transcriptional JJ 241 254 up-regulation up-regulation NN 255 257 of of IN 258 261 the the DT 262 284 c-sis/platelet-derived c-sis/platelet-derived JJ 285 291 growth growth NN 292 300 factor-B factor-b NN 301 302 ( ( ( 302 308 PDGF-B PDGF-B NNP 308 309 ) ) ) 310 324 proto-oncogene proto-oncogene NN 325 327 by by IN 328 331 the the DT 332 335 Tax Tax NNP 336 343 protein protein NN 344 346 of of IN 347 352 human human JJ 353 359 T-cell t-cell NN 360 368 leukemia leukemia NN 369 374 virus virus NN 375 379 type type NN 380 381 1 1 CD 382 385 has have VBZ 386 390 been be VBN 391 401 implicated implicate VBN 402 404 as as IN 405 408 one one CD 409 417 possible possible JJ 418 427 mechanism mechanism NN 428 430 of of IN 431 439 cellular cellular JJ 440 454 transformation transformation NN 455 457 by by IN 458 463 human human JJ 464 470 T-cell t-cell NN 471 479 leukemia leukemia NN 480 485 virus virus NN 486 490 type type NN 491 492 1 1 CD 492 493 . . . 494 496 In in IN 497 505 previous previous JJ 506 510 work work NN 510 511 , , , 512 514 we we PRP 515 525 identified identify VBD 526 528 an an DT 529 538 essential essential JJ 539 543 site site NN 544 546 in in IN 547 550 the the DT 551 563 c-sis/PDGF-B c-sis/pdgf-b NN 564 572 promoter promoter NN 572 573 , , , 574 588 Tax-responsive tax-responsive JJ 589 596 element element NN 597 598 1 1 CD 599 600 ( ( ( 600 604 TRE1 TRE1 NNP 604 605 ) ) ) 605 606 , , , 607 616 necessary necessary JJ 617 620 for for IN 621 636 transactivation transactivation NN 637 639 by by IN 640 643 Tax Tax NNP 643 644 . . . 645 647 We we PRP 648 652 also also RB 653 663 identified identify VBD 664 667 Sp1 Sp1 NNP 667 668 , , , 669 672 Sp3 Sp3 NNP 672 673 , , , 674 677 and and CC 678 690 NGFI-A/Egr-1 ngfi-a/egr-1 NN 691 693 as as IN 694 697 the the DT 698 705 primary primary JJ 706 713 nuclear nuclear JJ 714 727 transcription transcription NN 728 735 factors factor NNS 736 743 binding bind VBG 744 746 to to TO 747 751 TRE1 TRE1 NNP 752 757 which which WDT 758 765 mediate mediate VBP 766 769 Tax Tax NNP 770 784 responsiveness responsiveness NN 784 785 . . . 786 788 In in IN 789 792 the the DT 793 800 present present JJ 801 805 work work NN 805 806 , , , 807 809 we we PRP 810 814 have have VBP 815 827 investigated investigate VBN 828 831 the the DT 832 844 mechanism(s) mechanism(s) NN 845 852 whereby whereby WRB 853 856 Tax Tax NNP 857 871 transactivates transactivate VBZ 872 875 the the DT 876 888 c-sis/PDGF-B c-sis/pdgf-b NN 889 903 proto-oncogene proto-oncogene NN 903 904 . . . 905 907 In in FW 908 913 vitro vitro FW 914 927 transcription transcription NN 928 934 assays assay NNS 935 941 showed show VBD 942 946 that that IN 947 950 Tax Tax NNP 951 954 was be VBD 955 959 able able JJ 960 962 to to TO 963 976 significantly significantly RB 977 985 increase increase VB 986 989 the the DT 990 1005 transcriptional transcriptional JJ 1006 1014 activity activity NN 1015 1017 of of IN 1018 1019 a a DT 1020 1028 template template NN 1029 1039 containing contain VBG 1040 1043 the the DT 1044 1048 -257 -257 CD 1049 1051 to to TO 1052 1055 +74 +74 CD 1056 1062 region region NN 1063 1065 of of IN 1066 1069 the the DT 1070 1082 c-sis/PDGF-B c-sis/pdgf-b NN 1083 1091 promoter promoter NN 1091 1092 . . . 1093 1108 Electrophoretic electrophoretic JJ 1109 1117 mobility mobility NN 1118 1123 shift shift NN 1124 1129 assay assay NN 1130 1138 analysis analysis NN 1139 1145 showed show VBD 1146 1150 that that IN 1151 1154 Tax Tax NNP 1155 1164 increased increase VBD 1165 1168 the the DT 1169 1172 DNA dna NN 1173 1180 binding binding NN 1181 1189 activity activity NN 1190 1192 of of IN 1193 1197 both both CC 1198 1201 Sp1 sp1 NN 1202 1205 and and CC 1206 1218 NGFI-A/Egr-1 ngfi-a/egr-1 NN 1219 1224 using use VBG 1225 1226 a a DT 1227 1231 TRE1 tre1 NN 1232 1237 probe probe NN 1237 1238 . . . 1239 1247 Analysis Analysis NNP 1248 1250 of of IN 1251 1254 Tax Tax NNP 1255 1262 mutants mutant NNS 1263 1269 showed show VBD 1270 1274 that that IN 1275 1278 two two CD 1279 1286 mutants mutant NNS 1286 1287 , , , 1288 1295 IEXC29S IEXC29S NNP 1296 1299 and and CC 1300 1308 IEXL320G IEXL320G NNP 1308 1309 , , , 1310 1314 were be VBD 1315 1321 unable unable JJ 1322 1324 to to TO 1325 1338 significantly significantly RB 1339 1352 transactivate transactivate VB 1353 1356 the the DT 1357 1369 c-sis/PDGF-B c-sis/pdgf-b NN 1370 1378 promoter promoter NN 1378 1379 . . . 1380 1387 Finally finally RB 1387 1388 , , , 1389 1411 co-immunoprecipitation co-immunoprecipitation NN 1412 1420 analysis analysis NN 1421 1429 revealed reveal VBD 1430 1434 that that IN 1435 1438 Tax Tax NNP 1439 1441 is be VBZ 1442 1446 able able JJ 1447 1449 to to TO 1450 1456 stably stably RB 1457 1461 bind bind VB 1462 1464 to to TO 1465 1469 both both CC 1470 1473 Sp1 sp1 NN 1474 1477 and and CC 1478 1490 NGFI-A/Egr-1 ngfi-a/egr-1 NN 1490 1491 . . . 1492 1505 Interestingly interestingly RB 1505 1506 , , , 1507 1529 co-immunoprecipitation co-immunoprecipitation NN 1530 1538 analysis analysis NN 1539 1543 also also RB 1544 1552 revealed reveal VBD 1553 1557 that that IN 1558 1561 Tax Tax NNP 1562 1568 mutant mutant NN 1569 1576 IEXC29S iexc29s NN 1577 1579 is be VBZ 1580 1586 unable unable JJ 1587 1589 to to TO 1590 1598 interact interact VB 1599 1603 with with IN 1604 1616 NGFI-A/Egr-1 ngfi-a/egr-1 NN 1616 1617 , , , 1618 1625 whereas whereas IN 1626 1629 Tax Tax NNP 1630 1636 mutant mutant NN 1637 1645 IEXL320G iexl320g NN 1646 1648 is be VBZ 1649 1653 able able JJ 1654 1656 to to TO 1657 1665 interact interact VB 1666 1670 with with IN 1671 1683 NGFI-A/Egr-1 ngfi-a/egr-1 NN 1683 1684 . . .