0 6 Single single JJ 7 11 cell cell NN 12 17 assay assay NN 18 20 of of IN 21 22 a a DT 23 36 transcription transcription NN 37 43 factor factor NN 44 51 reveals reveal VBZ 52 53 a a DT 54 63 threshold threshold NN 64 66 in in IN 67 80 transcription transcription NN 81 90 activated activate VBN 91 93 by by IN 94 101 signals signal NNS 102 111 emanating emanate VBG 112 116 from from IN 117 120 the the DT 121 127 T-cell t-cell NN 128 135 antigen antigen NN 136 144 receptor receptor NN 144 145 . . . 147 158 Stimulation stimulation NN 159 161 of of IN 162 163 T t NN 164 175 lymphocytes lymphocyte NNS 176 183 through through IN 184 189 their their PRP$ 190 197 antigen antigen NN 198 206 receptor receptor NN 207 212 leads lead VBZ 213 215 to to TO 216 219 the the DT 220 230 appearance appearance NN 231 233 of of IN 234 241 several several JJ 242 255 transcription transcription NN 256 263 factors factor NNS 263 264 , , , 265 274 including include VBG 275 280 NF-AT NF-AT NNP 281 284 and and CC 285 293 NF-kappa NF-kappa NNP 294 295 B B NNP 295 296 , , , 297 302 which which WDT 303 306 are be VBP 307 315 involved involve VBN 316 318 in in IN 319 329 regulating regulate VBG 330 335 genes gene NNS 336 344 required require VBN 345 348 for for IN 349 360 immunologic immunologic JJ 361 371 activation activation NN 371 372 . . . 373 375 To to TO 376 387 investigate investigate VB 388 391 the the DT 392 400 activity activity NN 401 403 of of IN 404 405 a a DT 406 412 single single JJ 413 426 transcription transcription NN 427 433 factor factor NN 434 436 in in IN 437 447 individual individual JJ 448 454 viable viable JJ 455 460 cells cell NNS 460 461 , , , 462 464 we we PRP 465 469 have have VBP 470 477 applied apply VBN 478 480 an an DT 481 486 assay assay NN 487 491 that that WDT 492 496 uses use VBZ 497 500 the the DT 501 523 fluorescence-activated fluorescence-activated JJ 524 528 cell cell NN 529 535 sorter sorter NN 536 538 to to TO 539 549 quantitate quantitate VB 550 568 beta-galactosidase beta-galactosidase NN 569 570 ( ( ( 570 578 beta-gal beta-gal JJ 578 579 ) ) ) 579 580 . . . 581 583 We we PRP 584 588 have have VBP 589 597 analyzed analyze VBN 598 601 the the DT 602 614 distribution distribution NN 615 617 of of IN 618 623 NF-AT NF-AT NNP 624 639 transcriptional transcriptional JJ 640 648 activity activity NN 649 654 among among IN 655 656 T t NN 657 662 cells cell NNS 663 673 undergoing undergo VBG 674 684 activation activation NN 685 687 by by IN 688 693 using use VBG 694 695 a a DT 696 705 construct construct NN 706 708 in in IN 709 714 which which WDT 715 720 three three CD 721 727 tandem tandem JJ 728 734 copies copy NNS 735 737 of of IN 738 741 the the DT 742 755 NF-AT-binding nf-at-binding JJ 756 760 site site NN 761 768 directs direct VBZ 769 782 transcription transcription NN 783 785 of of IN 786 789 the the DT 790 794 lacZ lacz NN 795 799 gene gene NN 799 800 . . . 801 813 Unexpectedly unexpectedly RB 813 814 , , , 815 826 stimulation stimulation NN 827 829 of of IN 830 836 cloned clone VBN 837 843 stably stably RB 844 855 transfected transfecte VBN 856 862 Jurkat Jurkat NNP 863 864 T t NN 865 870 cells cell NNS 871 876 leads lead VBZ 877 879 to to TO 880 881 a a DT 882 889 bimodal bimodal JJ 890 897 pattern pattern NN 898 900 of of IN 901 909 beta-gal beta-gal JJ 910 920 expression expression NN 921 923 in in IN 924 929 which which WDT 930 934 some some DT 935 940 cells cell NNS 941 948 express express VBP 949 951 no no DT 952 960 beta-gal beta-gal JJ 961 964 and and CC 965 971 others other NNS 972 979 express express VBP 980 984 high high JJ 985 991 levels level NNS 991 992 . . . 993 997 This this DT 998 1008 expression expression NN 1009 1016 pattern pattern NN 1017 1023 cannot cannot MD 1024 1026 be be VB 1027 1036 accounted account VBN 1037 1040 for for IN 1041 1043 by by IN 1044 1054 cell-cycle cell-cycle JJ 1055 1063 position position NN 1064 1066 or or CC 1067 1076 heritable heritable JJ 1077 1086 variation variation NN 1086 1087 . . . 1088 1095 Further far JJR 1096 1103 results result NNS 1103 1104 , , , 1105 1107 in in IN 1108 1113 which which WDT 1114 1122 beta-gal beta-gal JJ 1123 1131 activity activity NN 1132 1134 is be VBZ 1135 1145 correlated correlate VBN 1146 1150 with with IN 1151 1164 NF-AT-binding nf-at-binding JJ 1165 1173 activity activity NN 1173 1174 , , , 1175 1183 indicate indicate VBP 1184 1188 that that IN 1189 1192 the the DT 1193 1206 concentration concentration NN 1207 1209 of of IN 1210 1215 NF-AT NF-AT NNP 1216 1220 must must MD 1221 1227 exceed exceed VB 1228 1229 a a DT 1230 1238 critical critical JJ 1239 1248 threshold threshold NN 1249 1255 before before IN 1256 1269 transcription transcription NN 1270 1279 initiates initiate NNS 1279 1280 . . . 1281 1285 This this DT 1286 1295 threshold threshold NN 1296 1302 likely likely RB 1303 1311 reflects reflect VBZ 1312 1315 the the DT 1316 1321 NF-AT nf-at NN 1322 1345 concentration-dependent concentration-dependent JJ 1346 1354 assembly assembly NN 1355 1357 of of IN 1358 1371 transcription transcription NN 1372 1381 complexes complex NNS 1382 1384 at at IN 1385 1388 the the DT 1389 1397 promoter promoter NN 1397 1398 . . . 1399 1406 Similar similar JJ 1407 1417 constructs construct NNS 1418 1428 controlled control VBN 1429 1431 by by IN 1432 1440 NF-kappa NF-kappa NNP 1441 1442 B B NNP 1443 1445 or or CC 1446 1449 the the DT 1450 1456 entire entire JJ 1457 1470 interleukin-2 interleukin-2 NN 1471 1479 enhancer enhancer NN 1480 1484 show show VBP 1485 1492 bimodal bimodal JJ 1493 1503 expression expression NN 1504 1512 patterns pattern NNS 1513 1519 during during IN 1520 1529 induction induction NN 1529 1530 , , , 1531 1541 suggesting suggest VBG 1542 1546 that that IN 1547 1557 thresholds threshold NNS 1558 1561 set set VBN 1562 1564 by by IN 1565 1568 the the DT 1569 1582 concentration concentration NN 1583 1585 of of IN 1586 1599 transcription transcription NN 1600 1607 factors factor NNS 1608 1611 may may MD 1612 1614 be be VB 1615 1616 a a DT 1617 1623 common common JJ 1624 1632 property property NN 1633 1635 of of IN 1636 1645 inducible inducible JJ 1646 1651 genes gene NNS 1651 1652 . . .