Regulation of Egr-1-dependent gene expression by the C-terminal activationdomain

The present study analyzes the role of the C-terminal activation domain for Egr-1 transcriptional activity using N-terminal deletion mutants. Mutant N 372 comprising the entire C-terminal activation domain and partly truncated DNA-binding and nuclear translocation domains functioned as the transdomin ant repressor of Egr-1-dependent gene transcription. Activity of the SV40 p romoter, however, was not affected by the N372 mutant. Analysis of addition al Egr-1 mutants revealed that the transdominant negative effect of N372 wa s dependent on truncation of the zinc finger motifs that mediate DNA bindin g. Reconstitution of the zinc fingers was sufficient to generate Egr-1 prot eins with potent transcriptional activity. The inhibitory mutant N372 is ef ficiently translocated to the nucleus, but fails to bind DNA and does not d isplace DNA-bound wildtype Egr-1. These results provide evidence for an Egr -1-specific cofactor that interacts with the C-terminal activation domain a nd is essential for Egr-1 transcriptional activity. (C) 1999 Academic Press .