Figure 8.

Nascent strand processing allows palindrome amplification via template switching in rad27Δ strains. (A) Two different subculture 25 strains are depicted, and the top sequence is mutated and includes a palindrome expansion. The bottom sequence is unchanged and includes an additional 17 bp (boxed). Arrows indicate palindromes. (B) DNA synthesis starts on a template similar to bottom sequence in A and continues until the fork is stalled. (C and D) An exonuclease then removes 17 bases. (E) The newly synthesized strand folds due to the homology between arms. A template switching occurs causing the nascent strand to use the recently synthesized arm as a template, expanding the palindrome. (F) The two DNA strands now differ in the area of expansion: the top strand resembles the bottom and original sequence in A, and the bottom strand resembles the top and mutated sequence in A. The next round of replication results in two daughter cells with the sequence changes that appear in A. The red strand is the nascent strand and the blue strand is the original template strand.