No abstract

To identify proteins that interact with Jun or Fos we have used the protein interaction cloning system developed by S. Fields and O.-K. Song [(1989) Nature (London) 340, [245][246] to clone mammalian cDNAs encoding polypeptides that interact with the dimerization and DNA-binding motif (bZIP; basic domain leucine zipper motif) ofJun. For this purpose, yeast cells lacking GAL4 activity but expressing a GAL4 DNA-binding domain-Jun bZIP fusion protein were transformed with a mouse embryo cDNA plasmid library in which the cDNA was joined to a gene segment encoding the GAL4 transcriptional activation domain. Several transformants exhibiting GAL4 activity were identified and shown to harbor plasmids encoding polypeptides predicted to form coiled-coil structures with Jun and/or Fos. One of these is a bZIP protein of the ATF/CREB protein family-probably the murine homolog of TAXREB67. Two others encode polypeptides with predicted potential to form coiled-coil structures, and seven other isolates encode segments of a-or f-tropomyosin, classical coiled-coil proteins. The tropomyosin polypeptides were found to interact in the yeast assay system with the bZIP region of Jun but not with the bZIP region of Fos. Our results illustrate the range of protein interaction cloning for discovering proteins that bind to a given target polypeptide.Jun and Fos are sequence-specific DNA-binding proteins that regulate transcription. Each protein has a bipartite DNAbinding domain [bZIP; basic domain leucine zipper motif (1)] consisting of an amphipathic helix that mediates dimerization through formation of a short coiled-coil structure (2), termed the "leucine zipper" (3), and an adjacent basic region that contacts DNA (4-6). Dimerization of monomers in a parallel orientation positions each basic region to interact with a half site of the DNA target sequence. In principle, a given bZIP transcription factor could interact with a variety of bZIP proteins with compatible amphipathic helices, yielding dimers with different DNA-binding and transcriptional properties (for review, see ref. 7). In the case of the known members of the Jun and Fos families, all pairwise combinations capable of forming dimers bind to the same dyad symmetric core sequence (8) (for reviews, see refs. 9 and 10), but their transcriptional properties often vary (11, 12). Moreover, the transcriptional activities ofJun can be modulated by interactions with other proteins, such as the glucocorticoid receptor (13-15), the inhibitory protein IP-1 (16), and a cell-specific inhibitor (17).The goal of the present study is to identify additional mammalian proteins that interact with Jun or Fos, some of which may form DNA-binding dimers with activities different from those of Jun-Fos heterodimers. For this purpose, we have used a yeast genetic system described by Fields and coworkers (18,19) in which expression of a GALJ-lacZ reporter gene under the control ofa GAL4-activated promotor depends on reconstitution of GAL4 activity via proteinprotein interaction. This is acc...

We have recently identified by cDNA cloning a set of genes that are rapidly activated in mouse 3T3 cells by serum or purified growth factors. Here we report that the cDNA (clone 268) derived from one of these immediate early genes (zif/268) encodes a protein with three tandem "zinc finger" sequences typical of a class of eukaryotic transcription factors. The mRNA of zif/268 is present in many organs and tissues of the mouse and is especially abundant in the brain and thymus tissue. The 5' genomic flanking sequence ofzif/268 has sequences related to binding sites for known regulatory proteins, including four sequences that resemble the core of the serum response elements (SREs) upstream ofthe c-fos and actin genes. The SRE-like sequences could be responsible for the coordinate activation ofzif/268 andfos after serum stimulation of 3T3 cells.

Expression of a set of growth-related immediate early genes in BALB/c 3T3 cells: Coordinate regulation with c-fos or c-myc (growth ABSTRACTWe have previously identified by cDNA cloning 5 mRNAs that appear in resting BALB/c 3T3 cells soon after growth stimulation by serum or platelet-derived growth factor. Five additional mRNAs of this class are described in this report. The mRNAs reached peak levels between 40 and 120 min after serum addition and rapidly decayed thereafter. All 10 RNAs were superinduced in the presence of cycloheximide.Nuclear run-on experiments indicated that the increase in the mRNAs is the result of rapid transcriptional activation of their genes on stimulation by serum or platelet-derived growth factor. Superinducibility by cycloheximide is due to two effects: prolonged transcription and stabilization of mRNAs. This overall pattern of regulation is similar to that of the c-fos or c-myc protooncogenes reported previously. We hypothesize that these newly identified "immediate early" genes play a role in the proliferative response induced by growth factors.The growth of mammalian cells is regulated by polypeptide growth factors (1). How such factors induce cell growth is a key question, relevant not only to the mechanisms of cell proliferation and neoplasia but more generally to the response of cells to a variety of extracellular ligands, such as developmental or differentiation factors, classical hormones, or neurotransmitters.

To identify previously undetected genes that may be involved in the transition from a resting state (G0) to a proliferative state (G1) of mammalian cells, we set out to isolate cDNA clones derived from mRNAs that appear in serum‐stimulated cells in the absence of protein synthesis. A lambda cDNA library was prepared using poly(A)+ RNA from BALB/c 3T3 cells that had been brought to quiescence and subsequently stimulated with serum in the presence of cycloheximide. Approximately 50 000 recombinant phage plaques were screened, and 357 clones were isolated that hybridized to probes derived from stimulated‐cell RNA but not to probes from resting‐cell RNA. Cross hybridization analysis showed that four RNA sequence families account for approximately 90% of these clones. One of the clones hybridized to an actin probe; none hybridized to any of 13 oncogene probes tested. Five different RNAs that appear to be previously uncharacterized have been further analyzed. These RNAs accumulate and decay rapidly following stimulation by serum or purified growth factors, or by a tumor promoter, and they are superinduced by serum in the presence of cycloheximide. Three of the RNAs could be enriched by hybridization to cDNAs and translated in vitro, yielding proteins of approximately 43, 40 and 35 kd, respectively.

A gene activated by growth factors is related to the oncogene v-jun (growth-related ABSTRACTWe have recently identified by cDNA cloning a set of genes that are rapidly activated in cultured mouse cells by protein growth factors. Here we report that the nucleotide sequence of a cDNA (clone 465)

Zif268, a zinc finger protein whose mRNA is rapidly activated in cells exposed to growth factors or other signaling agents, is thought to play a role in regulating the genetic program induced by extracellular ligands. We report that Zif268 has one of the characteristics of a transcriptional regulator, namely, sequence-specific binding to DNA. Zif268 synthesized in Escherichia coli bound to two sites upstream of the zif268 gene and to sites in the promoter regions of other genes. The nucleotide sequences responsible for binding were defined by DNase I footprinting, by methylation interference experiments, and by use of synthetic oligonucleotides. From these results we derived the following consensus sequence for a G Zi268 high-affinity binding site: GCGTGGGCG.

A gene inducible by serum growth factors encodes a member of the steroid and thyroid hormone receptor superfamily (