Characterization of the v-mybDNA binding domain

Abstract

The transforming protein encoded by the v-myb oncogene is a sequence-specific DNA-binding protein that is thought to be involved in the regulation of gene expression. The N-terminal region of the v-myb protein is composed of two highly conserved tandem repeat sequences of unknown function. It has been speculated that the N-terminal v-myb repeats might be crucial for DNA-binding, since N-terminal deletions destroy the DNA-binding activity of the v-myb protein. Here, we have studied the v-myb DNA-binding domain in more detail. Our results show that the N-terminal region of the v-myb protein is sufficient for specific DNA-binding. Dissection of this region suggests that both repeats are required for DNA-binding, but that both repeats play different roles in v-myb protein DNA interaction. We also show that the myb repeats of a drosophila melanogaster homolog of c-myb function as sequence-specific DNA-binding domain. Our results support the view that specific sequence-recognition, mediated by the conserved myb repeats, is a general feature of myb-related proteins.

Identification of functional domains in the maize transcriptional activator C1: comparison of wild-type and dominant inhibitor proteins.

“…These results, together with the results discussed above, provide in vivo evidence that the product of the Cl gene functions as a transcriptional activator that utilizes a myb-like DNAbinding domain with an acidic transcriptional activation domain. The basic domain of myb oncogene products consists of three imperfect repeats of 51-52 amino acids (Gerondakis and Bishop 1986;Rosson and Reddy 1986), and this domain has been shown to bind both specifically and nonspecifically to DNA (Oehler et al 1990). Deletion analysis of the myb DNA-binding region was used to demonstrate that the first repeat (missing from the maize Cl protein) is not essential for DNA binding, whereas the second and third repeats are crucial for specific site recognition (Howe et al 1990;Oehler et al 1990).…”

“…The basic domain of myb oncogene products consists of three imperfect repeats of 51-52 amino acids (Gerondakis and Bishop 1986;Rosson and Reddy 1986), and this domain has been shown to bind both specifically and nonspecifically to DNA (Oehler et al 1990). Deletion analysis of the myb DNA-binding region was used to demonstrate that the first repeat (missing from the maize Cl protein) is not essential for DNA binding, whereas the second and third repeats are crucial for specific site recognition (Howe et al 1990;Oehler et al 1990). Several myb oncogene products have been reported to function as transcriptional activators that act through specific DNA-binding sites (Ness et al 1989;Nishina et al 1989;Sakura et al 1989;Ibanez and Lipsick 1990).…”

B-Myb function can be markedly enhanced by cyclin A-dependent kinase and protein truncation

“…The Myb proteins are localised to the cell nucleus and bind a PyAACG/TG consensus DNA sequence (Biedenkapp et al, 1988), designated the Myb binding site (MBS). DNA-binding is mediated through a comparatively large aminoterminal domain (Howe et al, 1990;Oehler et al, 1990) which demonstrates a high degree of conservation within this protein family. All three members of the Myb protein family have been reported to activate transcription from responsive promoters (Nishina et al, 1989;Weston and Bishop, 1989;Mizuguchi et al, 1990;Foos et al, 1994;Golay et al, 1994;Ma and Calabretta, 1994;Takahashi et al, 1995), however, there are distinct di erences in their transcription regulatory properties, particularly between c-Myb and B-Myb.…”

Oncogenic truncation of the first repeat of c-Myb decreases DNA binding in vitro and in vivo.

“…The individual repeats have no clear homology to other known DNA-binding motifs, although similarities to the helix-turn-helix structure of the homeodomain proteins and the basic region of the bZIP proteins have been proposed (7,17,53). Interestingly, the first repeat and most of the second repeat are not required for sequence-specific DNA binding (18,27,52 although v-Myb lacks most of the first repeat (72). Nevertheless, all three of these repeats have been highly conserved during the evolution of vertebrates, invertebrates, and the cellular slime mold Dictyostelium discoideum (reference 65 and references therein).…”