Schematic representation of the CES-2, TEF, DBP, HLF, E2A-HLF, and E4BP4/NFIL3 proteins. The CES-2 protein in C elegans contains a basic region/leucine zipper (bZIP) domain in the carboxyl-terminal region and acts as a transrepressor. TEF, DBP, and HLF contain a proline- and acidic amino acid–rich (PAR) domain as well as a bZIP domain in the carboxyl-terminal region, which shows high level of sequence identity to that of CES-2. TEF, DBP, and HLF each also contain a trans-activation domain (TAD) and can act as transcriptional activators. The E2A-HLF fusion protein, which is expressed in t(17;19)–positive leukemia cells, retains the 2 transactivation domains in the amino terminal of E2A (AD1 and AD2) but not its basic region/helix-loop-helix domain, which is replaced by the bZIP domain of HLF. E2A-HLF has a joining region (▪ with arrowhead) generated at the breakpoint but not the basic region extension (BRE; indicated with ▤) nor the PAR domain of HLF, which contribute to sequence-specific DNA binding. E4BP4/NFIL3 contains a bZIP domain in its amino-terminal region and has nearly identical DNA-binding specificity as that of CES-2, TEF, DBP, HLF, and E2A-HLF. E4BP4 acts as either a transactivator or transrepressor depending on complexes formed by its TAD or transrepression domain (TRD) in its carboxyl-terminal region.