Antisense overlapping open reading frames in genes from bacteria to humans

Long Open Reading Frames (ORFs) in antisense DNA strands have been reported in the literature as being rare events. However, an extensive analysis of the GenBank database revealed that a substantial number of genes from several species contain an in-phase ORF in the antisense strand, that overlaps entirely the coding sequence of the sense strand, or even extends beyond. The findings described in this paper show that this is a frequent, non-random phenomenon, which is primarily dependent on codon usage, and to a lesser extent on gene size and GC content. Examination of the sequence database for several prokaryotic and eukaryotic organisms, demonstrates that coding sequences with in-phase, 100% overlapping antisense ORFs are present in every genome studied so far.