Somatic mutations in c-myc intron I cluster in discrete domains that define protein binding sequences.
The activated c-myc allele in Burkitt's lymphoma tumor cells is associated with a clustering of somatic mutations within intron I near the exon I boundary. We have identified several discrete protein binding sites within this region of c-myc intron I designated as myc intron factor-1 (MIF-1), MIF-2, and MIF-3. In addition to our previous characterization of a 20-nucleotide binding site for MIF-1, we now have identified adjacent 20-nucleotide and 34-nucleotide binding sites for MIF-2 and MIF-3, respectively. All three elements are protected from exonuclease digestion by nuclear protein extracts, and each gives rise to a distinct migration pattern on mobility shift assays. In addition, MIF-1, 2, and 3 share a 5-nucleotide (TTATG) internal sequence, which may account for cross-competition of these binding sites in the exonuclease protection experiment. Deletion mutant analyses showed that selective removal of the MIF-3 binding site alone was sufficient to enhance chloramphenicol acetyltransferase reporter activity similar to that observed with larger deletions of myc intron I. We have demonstrated that somatic mutations in activated c-myc alleles are frequently clustered in discrete domains that define protein recognition sequences.
Yu
B W
BW
Medicine Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892.
Ichinose
I
I
Bonham
M A
MA
Zajac-Kaye
M
M
D001482:Base Composition; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D005091:Exons; D016259:Genes, myc; D006367:HeLa Cells; D006801:Humans; D007438:Introns; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009838:Oligodeoxyribonucleotides / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection; D014407:Tumor Cells, Cultured
D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase