Identification of an internal gene to the human galectin-3 gene with two different overlapping reading frames that do not encode galectin-3

We previously reported that alternative transcripts were initiated within t he second intron of the human Galectin-3 gene (LGALS3), We now demonstrate that these transcripts arise from an internal gene embedded within LGALS3 a nd named galig (Galectin-3 internal gene). Tissue-specific expression of ga lig was assayed by screening of several human tissues. Contrary to LGALS3, galig appears to be tightly regulated and principally activated in leukocyt es from peripheral blood. Cloning and characterization of galig transcripts revealed that they contain two out-of-frame overlapping open-reading frame s (ORFs). Transfection of expression vectors encoding enhanced green fluore scent protein (EGFP) chimeras indicated that both ORFs could be translated in proteins unrelated to Galectin-3. The ORF1 polypeptide targets EGFP to c ytosol and nucleus whereas ORF2 targets EGFP to mitochondria. These results revealed the exceptional genetic organization of the LGALS3 locus.