In situ hybridization reveals that the product of a known oncogene, inserted into a mouse egg cell, hybridizes to multiple copies of RNA (black spots).

In the case of chromosome translocations, a proto-oncogene on one chromosome might be moved to another chromosome, resulting in the gene's structural alteration and/or aberrant expression. For example, in the translocation between chromosomes 9 and 22 that is found in CML, a proto-oncogene on chromosome 9, called c-Abl, is moved to chromosome 22, where it is fused to another gene called Bcr. Normally, c-Abl is a nuclear enzyme called "tyrosine kinase," which adds a phosphate molecule to proteins at an amino acid called tyrosine. Phosphorylation regulates the function of certain proteins that play important roles in stimulating cell proliferation. The fusion of Bcr and c-Abl genes creates an oncogene, called Bcr/Abl, which makes a highly overactive tyrosine kinase variant that is found in the cytoplasm instead of the nucleus. These changes in the activity and cellular location of the c-Abl proto-oncogene lead to chronic myelogenous leukemia.

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