0 1 A a DT 2 5 new new JJ 6 12 member member NN 13 15 of of IN 16 19 the the DT 20 27 leucine leucine NN 28 34 zipper zipper NN 35 40 class class NN 41 43 of of IN 44 52 proteins protein NNS 53 57 that that WDT 58 63 binds bind VBZ 64 66 to to TO 67 70 the the DT 71 74 HLA HLA NNP 75 77 DR DR NNP 78 83 alpha alpha NN 84 92 promoter promoter NN 92 93 . . . 95 102 Several several JJ 103 110 mutants mutant NNS 111 118 derived derive VBN 119 123 from from IN 124 135 transformed transform VBN 136 141 human human JJ 142 143 B B NNP 144 148 cell cell NN 149 154 lines line NNS 155 158 are be VBP 159 168 defective defective JJ 169 171 in in IN 172 182 expressing express VBG 183 188 major major JJ 189 207 histocompatibility histocompatibility NN 208 215 complex complex NN 216 217 ( ( ( 217 220 MHC MHC NNP 220 221 ) ) ) 222 227 class class NN 228 230 II ii CD 231 236 genes gene NNS 236 237 . . . 238 241 The the DT 242 249 failure failure NN 250 252 to to TO 253 260 express express VB 261 262 a a DT 263 268 class class NN 269 271 II ii CD 272 276 gene gene NN 277 279 in in IN 280 282 at at IN 283 288 least least JJS 289 292 one one CD 293 297 such such JJ 298 304 mutant mutant JJ 305 309 line line NN 310 313 has have VBZ 314 318 been be VBN 319 325 mapped map VBN 326 328 to to TO 329 332 the the DT 333 336 MHC MHC NNP 337 342 class class NN 343 345 II ii CD 346 347 X X NNP 348 351 box box NN 351 352 , , , 353 354 a a DT 355 364 conserved conserve VBN 365 380 transcriptional transcriptional JJ 381 388 element element NN 389 391 in in IN 392 395 the the DT 396 404 promoter promoter NN 405 411 region region NN 411 412 . . . 413 414 A a DT 415 428 complementary complementary JJ 429 432 DNA dna NN 433 441 encoding encode VBG 442 443 a a DT 444 455 DNA-binding dna-binding JJ 456 463 protein protein NN 464 465 ( ( ( 465 470 human human JJ 471 472 X x NN 473 476 box box NN 477 484 binding binding NN 485 492 protein protein NN 492 493 , , , 494 500 hXBP-1 hxbp-1 NN 500 501 ) ) ) 502 507 whose whose WP$ 508 514 target target NN 515 517 is be VBZ 518 521 the the DT 522 527 human human JJ 528 530 DR dr NN 531 536 alpha alpha NN 537 538 X x NN 539 542 box box NN 543 546 and and CC 547 550 the the DT 551 552 3 3 CD 552 553 ’ ' SYM 554 562 flanking flanking NN 563 569 region region NN 570 573 has have VBZ 574 577 now now RB 578 582 been be VBN 583 589 cloned clone VBN 589 590 . . . 591 595 This this DT 596 609 complementary complementary JJ 610 613 DNA dna NN 614 621 encoded encode VBD 622 623 a a DT 624 631 protein protein NN 632 636 with with IN 637 647 structural structural JJ 648 660 similarities similarity NNS 661 663 to to TO 664 667 the the DT 668 673 c-jun c-jun NN 674 688 proto-oncogene proto-oncogene NN 689 696 product product NN 696 697 , , , 698 701 and and CC 702 705 its its PRP$ 706 712 target target NN 713 721 sequence sequence NN 722 725 was be VBD 726 733 closely closely RB 734 741 related related JJ 742 744 to to TO 745 748 the the DT 749 760 palindromic palindromic JJ 761 767 target target NN 768 776 sequence sequence NN 777 779 of of IN 780 785 c-jun c-jun NN 785 786 . . . 787 795 Mutation mutation NN 796 798 of of IN 799 802 the the DT 803 809 hXBP-1 hxbp-1 NN 810 813 DNA dna NN 814 820 target target NN 821 829 sequence sequence NN 830 839 decreased decrease VBD 840 842 DR DR NNP 843 848 alpha alpha NN 849 857 promoter promoter NN 858 866 activity activity NN 867 869 in in FW 870 874 vivo vivo FW 874 875 . . . 876 881 These these DT 882 889 studies study NNS 890 897 suggest suggest VBP 898 902 that that IN 903 906 the the DT 907 913 hXBP-1 hxbp-1 NN 914 921 protein protein NN 922 926 acts act VBZ 927 929 as as IN 930 931 a a DT 932 945 transcription transcription NN 946 952 factor factor NN 953 955 in in IN 956 957 B B NNP 958 963 cells cell NNS 963 964 . . .