A POTENTIAL ROLE FOR ELF-1 IN TERMINAL TRANSFERASE GENE-REGULATION

The terminal deoxynucleotidyltransferase (TdT) gene represents an attr active model for the analysis of gene regulation during an early phase of lymphocyte development. In previous studies, we identified a DNA e lement, termed D', which is essential for TdT promoter activity in imm ature lymphocytes, and two classes of D'-binding factors, Ikaros prote ins and Ets proteins, Here, we report a detailed mutant analysis of th e D' element which suggests that an Ets protein, rather than an Ikaros protein, activates TdT transcription, Since multiple Ets proteins are expressed in developing lymphocytes and are capable of binding to the D' element, DNA affinity chromatography was used to determine if one of the Ets proteins might bind to the D' element with a uniquely high affinity, thereby implicating that protein as a potential TdT activato r, Indeed, one binding activity was greatly enriched in the high-salt eluates from a D' affinity column, Peptide microsequencing revealed th at the enriched protein was Elf-1. Immunoblot analyses confirmed that in nuclear extracts, Elf-1 has a significantly higher affinity for the D' sequence than does another Ets protein, Ets-1. Transactivation and expression studies support the hypothesis that Elf-1 activates TdT tr anscription in immature T and B cells, Finally, a D' mutation which se lectively reduces Elf-1 binding, hut not the binding of other Ets prot eins, was found to greatly reduce TdT promoter activity, Although Elf- 1 previously had been implicated in the inducible activation of genes in mature T and B cells, our results suggest that it also plays an imp ortant role in regulating genes during an early phase of lymphocyte de velopment.