Codon Usage and the Origin of P Elements

Abstract

The authors of a recent comparison of the P transposable element and three genes of Drosophila melanogaster and Drosophila willistoni suggested that the codon usage of the D. melanogaster P element is similar to that of D. willistoni genes (Powell and Gleason 1996 ). They concluded that this could be further evidence of the recent horizontal transfer of the P element from D. willistoni to D. melanogaster indicated by several previous findings (Clark and Kidwell 1997 ). More specifically, it was shown that D. willistoni genes tend to be T-ending-codon genes, whereas those of D. melanogaster tend to be C-ending-codon genes. The transposase genes of the P elements from both species was found to be AT-ending-codon genes, and one explanation for this may be that the P element of D. melanogaster originated from D. willistoni. This hypothesis assumes that the codon usage in transposable elements (TEs) and that in the host genome are similar. However, analysis of a large number of genes and TEs in D. melanogaster suggests that the T-ending-codon feature of the P element could be a general characteristic of all TEs in Drosophila species and independent of the host genome (Shields and Sharp 1989 ).