In vitro genetic techniques were used to study the sequence requirements for the initiation of specific transcription. Deletion mutants were constructed around the putative promoter of the adenovirus-2 major late and chicken conalbumin genes. Specific transcription in vitro by RNA polymerase B together with a HeLa cell cytoplasmic extract was used as the test for promoter function. With this approach sequences which are essential for the initiation of specific transcription in vitro, were shown to be located between 12 and 32 base pairs upstream from the 5′ end of these genes.

By introduction of recombinant plasmids into monkey CV1 cells, we have unambiguously demonstrated that sequences entirely within the 72 bp repeat, which is located upstream of the SV40 early region, are crucial for T-antigen expression in vivo. We have also shown that a DNA fragment containing the 72 bp repeat, inserted directly before chicken conalbumin or adenovirus-2 major late promoter sequences in chimeric plasmids where these promoters replace that of the SV40 early genes, caused a dramatic increase in the expression of T-antigen in vivo. This effect was independent of the orientation of the 72 bp repeat, but was sensitive to its location within the plasmid, when the 72 bp repeat was separated from the promoter sequences, T-antigen expression was reduced. Insertion of the 72 bp repeat into equivalent plasmids containing no known eukaryotic promoter sequences (plasmids which were not detectably expressed in vivo) gave rise to a measurable, but smaller level of expression. The stimulation of expression by the 72 bp repeat is cis-acting : it required covalent linkage to the recombinant. We discuss the possibility that the 72 bp repeat region in SV40 may act as a bi-directional entry site for RNA polymerase B such that promoter sequences linked to the repeat are more efficiently utilised.

Interest in the Ets proteins has grown enormously over the last decade. The v‐ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a ceilular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so‐called ‘ets domain’. The ets domain has been shown to be a DNA‐binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein–protein interactions with co‐factors that help determine its biological activity. Many of the Ets‐related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti‐oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets‐like proteins may have other functions, such as in DNA replication and a general role in transcription activation.Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T‐cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors, G‐proteins, kinases and transcription factors. We will discuss how several Ets‐related proteins fit into this scheme, and how their activity is regulated both post‐and pre‐translationally. Loss of normal control is often associated with conversion to an onco‐protein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene‐related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets‐family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.