, 1999). RecA*, besides assisting in LexA self-cleavage, also facilitates the intermolecular self-cleavage of UmuD2 (Burckhardt et al., 1988; Nohmi et al., 1988; Shinagawa et al., 1988). Cleaved UmuD′2 bound to UmuC (Woodgate et al., 1989) forms DNA polymerase V about 20–40 min after DNA damage (Sommer et al., 1998). Pol V carries out translesion replication of damaged DNA, but lacks 3′-5′ exonuclease activity, and thus is error prone (Tang et al.,

1999), resulting in SOS mutagenesis. Research in non-E. coli species reveals variation in LexA function and number, as well as different SOS genes and SOS boxes bound by LexA. In Acinetobacter baylyi RAD001 strain ADP1, additional differences also exist. In ADP1, recA (Rauch et al., 1996) and ddrR (a gene of unknown function that is unique to the Acinetobacter genus; Hare et al., 2006, 2012) are induced after DNA damage, but only ddrR requires RecA for induction (Whitworth, 2000). The ADP1 recA and ddrR promoters also lack a known or predicted SOS box (Gregg-Jolly & Ornston, 1994; Hare et al., 2006). Additionally, typical DNA damage response genes AZD9291 order encoding

LexA, SulA, or sigma factor σ38 are not found in A. baylyi or Acinetobacter baumannii (Hare et al., 2006; Robinson et al., 2010), and accordingly, SOS mutagenesis has not been observed in Acinetobacter (Berenstein, 1987) with the notable exception of the emerging pathogens A. baumannii and Acinetobacter ursingii (Hare et al., 2012). Further C-X-C chemokine receptor type 7 (CXCR-7) differences are centered on the umuDC operon in Acinetobacter. In ADP1, A. baumannii, and seven other Acinetobacter species examined, the umuD homolog (termed umuDAb; Hare

et al., 2012) encodes an extra 59-aa N-terminus region relative to the typical bacterial umuD and is always located adjacent to ddrR. Conversely, umuDC operons similar in size to those found in E. coli are present in only 50% of Acinetobacter species studied, seemingly acquired through horizontal gene transfer (Hare et al., 2012). Also unlike typical UmuD function, this newly described umuDAb allele regulates transcription of the adjacent DNA damage–induced ddrR gene (Hare et al., 2006), as well as other genes (J. M. Hare and J. A. Bradley, unpublished data) in ADP1. This Acinetobacter UmuDAb possesses both the conserved serine–lysine catalytic dyad required by UmuD, LexA, and some bacteriophage repressors for self-cleavage (Paetzel et al., 1997; Walker, 2001) as well as the (Ala/Cys)-Gly cleavage site (Hare et al., 2006, 2012), which suggests that UmuDAb may self-cleave by a similar mechanism. The regulatory activity and possession of an N-terminal domain (Hare et al., 2006) that both UmuDAb and LexA possess further predict that UmuDAb may conduct intramolecular cleavage like LexA, instead of the intermolecular cleavage of UmuD2 (McDonald et al., 1998) that is required for its participation in SOS mutagenesis.