The ternary complex factor Elk-1 belongs to the Ets oncoprotein family
. We demonstrate that this transcription factor is localized predomina
ntly in the nucleus, for which at least two regions of Elk-I are requi
red. One of these regions is part of the N-terminal ETS-domain, while
the other encompasses amino acids 137-157. In conjunction with the ETS
-domain, which mediates autonomous binding of Elk-1 to some DNA target
sequences, the conserved B-region is both necessary and sufficient fo
r ternary complex formation with the c-fos serum response element and
the serum response factor. However, the B-region must be linked to the
ETS-domain by a spacer. Furthermore, the B-region impedes autonomous
DNA-binding, possibly by masking the ETS-domain. A point mutation with
in the ETS-domain, homologous to the ts1.1 point mutation of v-Ets in
the E26 virus, affects DNA-binding of Elk-1 in a temperature-dependent
manner, which by analogy might be causative for the altered phenotype
of ts1.1 E26. Finally we show that amino acids 83-428 contribute to E
lk-1 mediated transactivation. In particular, the region 376-404 is in
dispensable for transactivation, while flanking amino acids on both si
des are only required for enhancement of transcriptional efficacy.