Importantly, in contrast to the highly error-prone Rev1/Polζ–mediated TLS that is observed in yeast (Lawrence &, Christensen, 1978, 1979; Lawrence et al, 1984; Gibbs et al, 2005; Acharya et al, 2006) or in TLS that occurs in mammalian cells during gap repair (Yoon et al, 2015), or in cancer cells (Doles et al, 2010; Xie et al, 2010; Xu et al, 2013), TLS dependent upon Polλ/Polζ operates in a predominantly error-free manner in human cells. Here, REV1 is linked to cancer.