Figure 8.

Evolution of mating-type switching. Left: same as Figure 7. Red lightning bolts refer to capture of site-specific nucleases. Right: MAT cassettes (colored boxes) are symbolized on chromosomes (gray bars) with MATa (horizontal black stripes) or MATα (vertical black stripes) idiomorphs. Silenced cassettes are shaded. Shown are the topologies observed in S. cerevisiae (for the Saccharomycetaceae) and K. phaffii (for the methylotrophs), but significant variations are found in both subgroups (see text). The α3 and Kat1 transposases of K. lactis are shown acting at the same place as the HO endonuclease of S. cerevisiae, despite important mechanistic differences.