Mechanisms for generating UV-induced recombinogenic DSBs.

Abstract

<p>At the top part of the figure, chromosomal DNA molecules are depicted as unreplicated double-stranded DNA molecules. Newly-synthesized DNA is depicted as gray dashed lines. UV-induced pyrimidine dimers are shown as triangles, and centromeres of replicated chromosomes are shown as ovals. A. Excision of a dimer results in a small gap and replication produces one broken and one unbroken sister chromatid. B. During replication of a DNA molecule with an unexcised dimer, a DSB occurs in one of the two sister chromatids. C. Excision of two closely-opposed dimers results in a short (<6 bp) unstable double-stranded region between the excision tracts. The resulting broken chromosome is replicated to form two broken sister chromatids. D. As in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003894#pgen-1003894-g009" target="_blank">Figure 9C</a>, two closely-opposed dimers are excised. One of the resulting short gaps is expanded by the 5′ to 3′ Exo1p nuclease (shown in green) to generate a broken chromosome. Replication of this chromosome results in two broken sister chromatids. E. The tract resulting form excision of a single dimer is expanded, leaving a large single-stranded DNA gap. An endonuclease cleaves this single-stranded region, resulting in two broken sister chromatids.</p