Identification of reciprocal translocation sites within the c-myc oncogene and immunoglobulin μ locus in a Burkitt lymphoma

The association between certain human tumours and characteristic chromosomal abnormalities has led to the hypothesis that specific cellular oncogenes¹ may be involved and consequently 'activated' in these genetic recombinations^2,3. This hypothesis has found strong support in the recent findings that some cellular homologues of retroviral onc genes are located in chromosomal segments which are affected by specific tumour-related abnormalities (see ref. 4 for review). In the case of human undifferentiated B-cell lymphoma (UBL) and mouse plasmacytomas, cytogenetic and chromosomal mapping data have identified characteristic chromosomal recombinations directly involving different immunoglobulin genes and the c-myc oncogene (for review see refs 5, 6). In UBLs carrying the t(8:14) translocation it has been shown that the human c-myc gene⁷ is located on the region of chromosome 8 (8q24) which is translocated to the immunoglobulin heavy-chain locus (IHC) on chromosome 14^8-10. Although it is known that the chromosomal breakpoints can be variably located within or outside the c-myc locus and within the IHC_μ (refs 9,11) or IHC_γ locus¹², the recombination sites have not been exactly identified and mapped in relation to the functional domains of these loci. We report here the identification and characterization of two reciprocal recombination sites between c-myc and IHC_μ in a Burkitt lymphoma. Nucleotide sequencing of the cross-over point joining chromosomes 8 and 14 on chromosome 14q- shows that the onc gene is interrupted within its first intron and joined to the heavy-chain μ switch region. This recombination predicts that the translocated onc gene would code for a rearranged mRNA but a normal c-myc polypeptide.