ds-Oligonucleotide–Peptide Conjugates Featuring Peptides from the Leucine-Zipper Region of Fos as Switchable Receptors for the Oncoprotein Jun

Fos and Jun family proteins regulate the expression of a myriad of genes in a variety of tissues and cell types. This functional versatility emerges from their interactions with related bZIP proteins and with structurally unrelated transcription factors. These interactions at composite regulatory elements produce nucleoprotein complexes with high sequence-specificity and regulatory selectivity. Several general principles including binding cooperativity and conformational adaptability have emerged from studies of regulatory complexes containing Fos-Jun family proteins. The structural properties of Fos-Jun family proteins including opposite orientations of heterodimer binding and the ability to bend DNA can contribute to the assembly and functions of such complexes. The cooperative recruitment of transcription factors, coactivators and chromatin remodeling factors to promoter and enhancer regions generates multiprotein transcription regulatory complexes with cell- and stimulus-specific transcriptional activities. The gene-specific architecture of these complexes can mediate the selective control of transcriptional activity.

The Fos and Jun families of eukaryotic transcription factors heterodimerize to form complexes capable of binding 5'-TGAGTCA-3' DNA elements. We have determined the X-ray crystal structure of a heterodimer of the bZIP regions of c-Fos and c-Jun bound to DNA. Both subunits form continuous alpha-helices. The carboxy-terminal regions form an asymmetric coiled-coil, and the amino-terminal regions make base-specific contacts with DNA in the major groove. Comparison of the two crystallographically distinct protein-DNA complexes show that the coiled-coil is flexibly joined to the basic regions and that the Fos-Jun heterodimer does not recognize the asymmetric 5'-TGAGTCA-3' recognition element in a unique orientation. There is an extensive network of electrostatic interactions between subunits within the coiled-coil, consistent with proposals that these interactions determine preferential formation of the heterodimer over either of the homodimers.

In eukaryotes, transcription of the diverse array of tens of thousands of protein-coding genes is carried out by RNA polymerase II. The control of this process is predominantly mediated by a network of thousands of sequence-specific DNA binding transcription factors that interpret the genetic regulatory information, such as in transcriptional enhancers and promoters, and transmit the appropriate response to the RNA polymerase II transcriptional machinery. This review will describe some early advances in the discovery and characterization of the sequence-specific DNA binding transcription factors as well as some of the properties of these regulatory proteins.