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. 1991 Oct;11(10):4918–4926. doi: 10.1128/mcb.11.10.4918-4926.1991

Highly conserved residues in the bZIP domain of yeast GCN4 are not essential for DNA binding.

W T Pu 1, K Struhl 1
PMCID: PMC361466  PMID: 1922025

Abstract

Yeast GCN4 and the Jun oncoprotein are transcriptional activators that bind DNA via a bZIP domain consisting of a leucine zipper dimerization element and an adjacent basic region that directly contacts DNA. Two highly conserved alanines (Ala-238 and Ala-239 in GCN4) and an invariant asparagine (Asn-235) in the basic region have been proposed to play important roles in DNA sequence recognition by bZIP proteins. Surprisingly, these conserved residues can be functionally replaced in GCN4 and in a derivative containing the Jun basic region (Jun-GCN4). The ability of an amino acid to functionally substitute for Asn-235 does not correlate with its preference for assuming the N-cap position of an alpha helix. This finding argues against the proposal of the scissors grip model that the invariant asparagine forms an N cap that permits the basic region to bend sharply and wrap around the DNA. In contrast to a prediction of the induced fork model, the pattern of functional substitutions of the conserved alanines together with the results of uracil interference experiments suggests that Ala-238 and Ala-239 do not make base-specific DNA contacts. Finally, the Jun-GCN4 chimeric proteins appear much more active in vivo than expected from their DNA-binding properties in vitro. The mechanistic and evolutionary implications of these results are discussed.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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