Transposon Invasion of the Paramecium Germline Genome Countered by a Domesticated PiggyBac Transposase and the NHEJ Pathway
Figure 3
Paramecium IES excision: a comparison with Tc1/mariner and piggyBac transposons. (a) Nucleotide sequence alignment of the ends of Paramecium IESs with the termini of Tc1 transposons (general Tc1/IS630 consensus and transposon families identified in Paramecium) and of the piggyBac element from Trichoplusia ni. Flanking sequences are in black (the conserved TA found at each boundary is highlighted in bold) and internal nucleotides are in red. Note that for piggyBac, the target site duplication is made of 4 base pairs (TTAA in black). (b) The geometry of double-strand DNA cleavages introduced by Tc1 (left) and piggyBac (right) transposases is shown on top, together with that of PiggyMac-dependent DSBs detected at Paramecium IES ends (middle). The conserved TAs are represented by black bold letters. Based on their transposition mechanism, Tc1 and piggyBac transposons are delimited by their cleaved 3′ ends and are represented by red lines. By analogy with Tc1, IESs are drawn as red lines bounded by two flanking TAs (in black), although this does not reflect the actual position of DNA cleavages. At the bottom of each panel, the structure of chromosomal junctions formed after excision from the donor site is shown. For Tc1 transposons and Paramecium IESs, the nucleotides that are neosynthesized during gap filling and repair are represented in blue.
