The response of a cell to mitogens and differentiation agents involves the transcriptional induction of several cellular genes. Prominent among these so-called 'immediate early' or 'competence' genes are the nuclear oncogenes fos and myc. Although the precise function of these early response genes in growth control is not understood, it is likely that many of them are involved in the transition from G0 to G1 in the cell cycle. The findings that the products of nuclear proto-oncogenes jun and erbA are transcriptional factors supports the notion of the role of the nuclear oncoproteins in the regulation of gene expression. Recently, it has been reported that the FOS protein is associated in transcriptional complexes with the product of the jun oncogene, the transcription factor AP-1. As the fos gene is induced in response to mitogens during initiation of cell growth, we investigated whether expression of the nuclear transcription factor AP-1 is also inducible. We report that mouse c-jun gene transcription is rapidly induced by serum and phorbol-ester 12-o-tetradecanoyl phorbol 13-acetate (TPA). Furthermore, induction is transient and the mRNA is superinduced by inhibitors of protein synthesis.

Murine gammaherpesvirus 68 (␥HV68) infects mice, thus providing a tractable small-animal model for analysis of the acute and chronic pathogenesis of gammaherpesviruses. To facilitate molecular analysis of ␥HV68 pathogenesis, we have sequenced the ␥HV68 genome. The genome contains 118,237 bp of unique sequence flanked by multiple copies of a 1,213-bp terminal repeat. The GC content of the unique portion of the genome is 46%, while the GC content of the terminal repeat is 78%. The unique portion of the genome is estimated to encode at least 80 genes and is largely colinear with the genomes of Kaposi's sarcoma herpesvirus (KSHV; also known as human herpesvirus 8), herpesvirus saimiri (HVS), and Epstein-Barr virus (EBV). We detected 63 open reading frames (ORFs) homologous to HVS and KSHV ORFs and used the HVS/KSHV numbering system to designate these ORFs. ␥HV68 shares with HVS and KSHV ORFs homologous to a complement regulatory protein (ORF 4), a D-type cyclin (ORF 72), and a G-protein-coupled receptor with close homology to the interleukin-8 receptor (ORF 74). One ORF (K3) was identified in ␥HV68 as homologous to both ORFs K3 and K5 of KSHV and contains a domain found in a bovine herpesvirus 4 major immediate-early protein. We also detected 16 methionine-initiated ORFs predicted to encode proteins at least 100 amino acids in length that are unique to ␥HV68 (ORFs M1 to 14). ORF M1 has striking homology to poxvirus serpins, while ORF M11 encodes a potential homolog of Bcl-2-like molecules encoded by other gammaherpesviruses (gene 16 of HVS and KSHV and the BHRF1 gene of EBV). In addition, clustered at the left end of the unique region are eight sequences with significant homology to bacterial tRNAs. The unique region of the genome contains two internal repeats: a 40-bp repeat located between bp 26778 and 28191 in the genome and a 100-bp repeat located between bp 98981 and 101170. Analysis of the ␥HV68, HVS, EBV, and KSHV genomes demonstrated that each of these viruses have large colinear gene blocks interspersed by regions containing virus-specific ORFs. Interestingly, genes associated with EBV cell tropism, latency, and transformation are all contained within these regions encoding virus-specific genes. This finding suggests that pathogenesis-associated genes of gammaherpesviruses, including ␥HV68, may be contained in similarly positioned genome regions. The availability of the ␥HV68 genomic sequence will facilitate analysis of critical issues in gammaherpesvirus biology via integration of molecular and pathogenetic studies in a small-animal model.

The c-Rel protein is able to associate in vitro and in vivo with the TATA-binding protein (TBP) of the TFIID complex. Coexpression of TBP with c-Rel augments transactivation from the kappa B site in Drosophila Schneider cells. DNA-binding mutants of TBP not only fail to cooperate, but they repress transactivation by c-Rel. There may be a direct communication between kappa B enhancer binding proteins and basal transcription factors which leads to enhanced transcription.

The bcl-3 gene product, overexpressed in chronic lymphocytic leukemia (CLL) patients with the translocation t(14;19), is a member of the IKB family. The bcl-3 protein is able to inhibit the DNA binding and trans-activation of authentic NF-KB heterodimers p50-p65 and p49-p65, as well as p50 and p49 homodimers. The bcl-3 protein does not inhibit either the DNA-binding activity of the Rel protein or its ability to trans-activate genes linked to the KB site. A human 37-kD protein (IKBa), identified previously as a member of the IKB family, is also unable to inhibit DNA-binding activity of the Rel protein. However, unlike bcl-3, the 37-kD (IKBa) protein has no effect on the DNA-binding activity of pS0 or p49 homodimers. Two dimensional phosphotryptic peptide maps of the human bcl-3 and the human 37-kD (IKBa) proteins reveal that the phosphopeptides from the 37-kD (IKBa) protein are nested within the bcl-3 protein.

The NF-B͞Rel proteins are sequestered in the cytoplasm in association with IB␣. In response to external signals, IB␣ is phosphorylated, multi-ubiquitinated, and degraded by proteasomes, thereby releasing NFB͞Rel proteins to migrate to the nucleus. We have cloned a mouse ubiquitin-conjugating enzyme (mE2), which associates with IB␣. mE2 is homologous to the yeast Ubc9͞Hus5 ubiquitin-conjugating enzyme. A transdominant-negative mutant of mE2 had no effect on phosphorylation of IB␣, but delayed its degradation. Correspondingly, tumor necrosis factor-␣-inducible NF-B activity was diminished. We propose that mE2 is directly involved in the ubiquitin conjugation of IB␣, a pivotal step in its degradation pathway.

Jun and Fos nuclear oncoproteins form a complex that regulates transcription from promoters containing activator protein AP-1 binding sites. The leucine-zipper and basic-region domains of both Fos and Jun are necessary for formation of the heterodimer that binds to DNA. Reciprocal mutations in the basic region of Fos or Jun can influence the binding of the heterodimer to DNA, implying a symmetrical binding site. DNA-binding mutants of Jun exhibit increased affinity for Fos and are capable of suppressing wild-type Fos-Jun DNA-binding activity. In contrast, mutations in the basic domain of Fos, which prevent binding to DNA in association with Jun, do not significantly diminish the ability of the wild-type heterodimer to bind to DNA. These dominant negative mutants are functional in vivo and can be exploited to study the role of Fos and Jun in normal and transformed cells.

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