Evolution of overlapping genes

Abstract

THE nucleotide sequence of the DNA of φX174 phage established by Sanger's group^1,2 has revealed that this phage has two overlapping genes in which the same stretch of DNA can code for two proteins which are translated in different reading frames. That two overlapping genes occur in the same DNA genome suggests that this overlapping expression is not unique to φX174 but of more general significance, at least in organisms with small DNA molecules. Once the overlapping expression is established, all mutations in one gene would also alter the other gene within the region of overlap. Some of these mutations, however, may affect one protein but not the other because of codon degeneracy. In general, the evolutionary constraints on a sequence representing both proteins must be very severe. In this report we estimate the extent to which the evolution of a gene is reduced by the acquisition of overlapping expression.