Expression of c‐myc proto oncogene is regulated by multiple mechanisms. Here, we report that the consensus of the regulatory region of interferondependent genes, GGAAAN1−3 GAAA, was found after computer search in the 5'‐terminal flank of human c‐myc gene in position (−76:−67). In vitro transcription of c‐myc gene fragments showed that the consensus region competes with oligonucleotide GGGAAAATGAAACT for binding to specific protein(s). This oligonucleotide was shown to bind selectively the interferon‐dependent positive transcription factor [1]. Transcription of c‐myc fragments lacking 5'‐terminal region up to positions −101 or +71 was initiated at two sites located in the first intron. These sites did not coincide with P1 in vivo RNA cap‐site. Binding of the protein factor(s) to the regulatory region of c‐myc gene −76:−67 blocked the in vitro transcription initiated in the first intron.

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The human c-myc proto-oncogene was recently found to contain a regulatory sequence similar to the consensus interferon-response sequence (IRS) of interferon-activating genes. Binding of regulatory protein(s) to this sequence of cloned fragment of c-myc, lacking the main part of 5'-nontranscribing region, regulates in vitro transcription from 11/12 initiation sites located in the first intron of the gene.Here, we have shown that HeLa S3 nuclear extract contains different protein factors, at least two, that bind preferentially to the IRS sequence of either the c-myc gene or the interferon-dependent 6-16 gene. Moreover, each of these factors 'cross-binds' to the region of the other gene, although affinity of this interaction is lower. Binding constants of these proteins to oligonucleotide fragments of c-myc and 6-16 genes were determined.In vitro transcription of the human full-length c-myc gene (i. e. the gene containing the complete 5'-noncoding region) initiated from 11/12 sites, that is controlled by the IRS region, was demonstrated to be blocked. A possible physiological role for the mechanisms described is discussed.Human and mouse genes sensitive to the action of interferon(s) (IFN) have been shown to contain a consensus sequence designed as an IRS [I -81 that binds IFN-dependent transcription factor(s) [9 -111. Initially, this sequence was detected in human leukocyte antigens and metallothionein genes [l], and then in a number of IFN-dependent genes; it was represented originally as follows: GAZAGGAGAAACT.Regulatory sequences similar to the IRS consensus have been described as being potent regulators of transcription. In particular, it was shown that transfection of the cells with a plasmid construction containing a YGRGRAANNGAACY site resulted in the IFN-dependent transcription of the plasmid DNA [5, 121. These authors proposed a consensus of IFNdependent genes as follows: GNgkAANNGAAACz [12]; this region binds an IFN-stimulating transcription factor(s). In the comprehensive presentation by Porter et al. [8], it was shown that GGGAAAATGAAACT oligonucleotide competes with the IRS region of the human 6-16 gene, but GGGAAAATGACACT (i. e. the oligonucleotide with one mismatch) does not. The competition was analyzed by a gelretardation technique: the data have shown a high level of specificity of factors binding to the IRS sequence.Recently we proposed the IRS consensus sequence to be as follows : GGAAAN -,GAAA [13]. This consensus differs from analogous sequences that were described previously (see above), which is why the computer search for this consensus showed the presence of corresponding regions in the regula- tory parts of genes that were not characterized earlier as IFNdependent. This group of genes includes the human protooncogene c-myc [13].The IRS consensus sequence in the human c-myc gene was located at position -76 to -67 (+ 1 indicates P i cap site): c-myc: GGAAA A GAAA consensus: GGAAA N 1 -3GAAA.Previously we have shown that regulatory protein(s) present in a HeLa S3 cell extract which binds to...