Translesion DNA synthesis (TLS) bypasses DNA lesions encountered during S-phase and is critical for cell survival after exposure to DNA-damaging agents. In humans, Rad6/Rad18 attaches single ubiquitin moieties (i.e., monoubiquitination) to proliferating cell nuclear antigen (PCNA) sliding clamps encircling primer/template (P/T) junctions that are stalled at DNA lesions. TLS occurs via PCNA monoubiquitination-independent and -dependent pathways, and both contribute to cell survival. The interaction of Rad6/Rad18 with PCNA is paramount to PCNA monoubiquitination and remains poorly defined. In particular, the location of the Rad6/Rad18 binding site on PCNA is unknown. Many PCNA-binding proteins, particularly DNA polymerases (pols), converge on PCNA encircling stalled P/T junctions in human cells, and all interact in a similar manner with the universal binding sites on PCNA. We reasoned the following: if Rad6/Rad18 utilizes the universal binding sites (or nearby sites), then PCNA monoubiquitination may be suppressed by pols involved in TLS. Results from quantitative studies reveal that (1) a Y-family pol (pol η) and a B-family pol (pol δ) critical to TLS each inhibit the transfer of ubiquitin from Rad6/Rad18 to PCNA and that (2) the observed inhibitions are dependent on the interaction of these pols with PCNA encircling DNA. These studies suggest that Rad6/Rad18 utilizes the universal PCNA-binding sites or nearby sites and, hence, competes for PCNA encircling DNA with pols η and δ and possibly other PCNA-binding proteins involved in TLS. These findings provide valuable insight into the nature of the interaction between Rad6/Rad18 and PCNA and have important implications for the division of human TLS pathways.

中文翻译：

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Rad6 / Rad18与DNA聚合酶η和δ竞争PCNA环绕DNA。

跨病损DNA合成（TLS）绕过了S期遇到的DNA损伤，对于暴露于DNA损伤剂后的细胞存活至关重要。在人类中，Rad6 / Rad18将单个泛素部分（即单泛素化）连接到包围在DNA损伤处停滞的引物/模板（P / T）连接的增殖细胞核抗原（PCNA）滑动夹具。TLS通过PCNA单泛素依赖性和非依赖性途径发生，两者均有助于细胞存活。Rad6 / Rad18与PCNA的相互作用对于PCNA单泛素化至关重要，并且定义仍然很差。特别地，Rad6 / Rad18结合位点在PCNA上的位置是未知的。许多PCNA结合蛋白，尤其是DNA聚合酶（pols），会聚在PCNA周围的人细胞中停滞的P / T连接处，所有这些都以类似的方式与PCNA上的通用结合位点相互作用。我们推断以下原因：如果Rad6 / Rad18利用通用结合位点（或附近的位点），则TLS中涉及的pols可能会抑制PCNA单泛素化。定量研究的结果表明（1）对TLS至关重要的Y家族pol（polη）和B家族pol（polδ）均抑制泛素从Rad6 / Rad18向PCNA的转移，并且（2）抑制作用取决于这些pols与包围PCNA的DNA的相互作用。这些研究表明，Rad6 / Rad18利用通用的PCNA结合位点或附近位点，并因此与polsη和δ以及可能与TLS相关的其他PCNA结合蛋白竞争包围PCNA的DNA。