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. 2021 May 26;12(6):809. doi: 10.3390/genes12060809

Figure 1.

Figure 1

Orientation of same-strand overlapping genes. (A) Overlapping gene with the downstream frame shifted one nucleotide 3′ with respect to the upstream frame. There are 3 types of codon position (cp): cp13 (bold character), in which the first codon position of the upstream frame overlaps the third codon position of the downstream frame; cp21 (underlined character), in which the second codon position of the upstream frame overlaps the first codon position of the downstream frame; cp32 (italic character), in which the third codon position of the upstream frame overlaps the second codon position of the downstream frame. (B) Overlapping gene with the downstream frame shifted two nucleotides 3′ with respect to the upstream frame. There are 3 types of codon position (cp): cp12 (bold character), in which the first codon position of the upstream frame overlaps the second codon position of the downstream frame; cp23 (underlined character), in which the second codon position of the upstream frame overlaps the third codon position of the downstream frame; cp31 (italic character), in which the third codon position of the upstream frame overlaps the first codon position of the downstream frame. According to the genetic code, a nucleotide substitution at first codon position causes an amino acid change in 95.4% of cases, at second position in 100% of cases, and at third position in 28.4% of cases.