RecA protein structures

FIGURE 25-34 RecA. (a) Nudeoprotein filament of RecA protein on single-stranded DNA, as seen with the electron microscope. The stri-ations indicate the right-handed helical structure of the filament, (b) Surface contour model of a 24-subunit RecA filament. The filament has six subunits per turn. One subunit is colored red to provide perspective (derived from PDB ID 2REB). 

RecA protein binds to single-stranded or gapped DNA. The complementary strand of the linear DNA pairs with a circular single strand. The other linear strand is displaced (left) or pairs with its complement in the circular duplex to yield a Holliday structure (right). 

Figure 27-24 Structures of RecA protein spiral filaments. (A) RecA protein filament formed on circular duplex DNA in the presence of ATP(Y-S), shadowed with Pt and seen by electron microscopy. (B) Diagram of RecA bound to duplex DNA in the presence of ATP(y-S), as determined by electron microscopy. RecA monomers are shown as spheres, but their exact shape is unknown. (C) Diagram of RecA spiral filament in crystals of RecA protein free of DNA, based on X-ray crystallographic data. Arrows indicated alignment of monomers. From Howard-Flanders, West, and Stasiak.536...

Reactions catalyzed by purified recA protein in vitro. RecA catalyzes a number of different reactions between DNA strands, all of them involving the unwinding and winding of base-paired structures, (a) D-loop formation by interaction between supercoiled circular duplex DNA and single-stranded DNA. (b) Strand exchange between a gapped circular duplex structure and a linear duplex structure, (c) Complex formation between two helices, one of which is gapped. 

Centore RC, Sandler SJ. UvrD limits the number and intensities of RecA-green fluorescent protein structures in Escherichia coli K-12. J. Bacteriol. 2007 189 2915-2920. 

DNA-strand exchange between a ssDNA and a duplex in which all G and C residues have been replaced by 2 -deoxyisoguanosine (iG) and 2 -deoxy-5-methyl-isocytidine MiC) by the E. coli RecA protein in vitro occurred at a similar rate and efficiency to unmodified DNA. This provides further potential for the role of iG and MiC in an expanded genetic code. Using ODNs rich in isoguanosine residues, Chaput and Switzer have shown that iG quintet structures may be formed from a metal-assisted hydrogen bond-mediated self-assembly process. The structures were stabilised particularly in the presence of Cs+ ions. 

These two sites contain identical 15-bp core sequences within which the recombination occurs. In a manner similar to that of the recA protein a homologous region is located by the complex of the Int (integrase) protein and IHF. Several molecules of Int protein bind and, together with the IHF protein, hold the phage DNA in a nucleosomelike structure (an intasome) in which the recombination occurs Strand cleavage... 

Story RM, Steitz TA. Structure of the recA protein-ADP complex. Nature 1992 355(6358) 374-376. 

Fig. 8. Basic requirements for Pol V-mediated translesion synthesis in vitro sorting out the published literature. The groups of Dr. Goodman (Goodman, 2002), Dr. Livneh (Livneh, 2001), and ourselves (Fujii et ai, 2004) have published work on the reconstitution of lesion bypass using Pol V and accessory factors. As outlined in this figure, the three studies differ in (i) the nature of the Pol V preparation and (ii) the structure of the primer template. The length of the single-stranded region downstream from the lesion site that appears to be a critical parameter (see text) is indicated for each substrate. Except for RecA protein that was found to be essential in all three studies, differences with respect to the requirements of SSB protein, ATP or ATP S, and the f3 clamp have been reported as discussed in the text and summarized in this figure.

Tfe-REC is quite small (24,543 Da, p/ 9.69) compared to its bacterial and eukaryotic counterparts, with the N- and C-terminal regions being obviously truncated (Fig. lb). The crystal structure of E. coli RecA protein-ADP complex revealed a major domain that bound to ATP and single- and double-stranded DNAs, and two smaller subdomains at the N and C termini protruded from the major domain. Deletion analysis of the N-terminal 33 amino acid residues of RecA... 

Mechanism. LexA protein normally blocks the expression of fifteen or more genes involved in DNA repair. RecA protein spedfidally binds to the singlestrands produced by physical or chemical damage to DNA (see RecomUnation for details of recA structure and DNA binding). The single-strand DNA-... 

FIGURE 25-37 Models for recombinational DNA repair of stalled replication forks. The replication fork collapses on encountering a DNA lesion (left) or strand break (right). Recombination enzymes promote the DNA strand transfers needed to repair the branched DNA structure at the replication fork. A lesion in a single-strand gap is repaired in a reaction requiring the RecF, RecO, and RecR proteins. Double-strand breaks are repaired in a pathway requiring the RecBCD enzyme. Both pathways require RecA. Recombination intermediates... 

General recombination in eukaryotes is believed to be similar to the process in prokaryotes. Several eukaryotic proteins have been discovered that closely resemble in both structure and function those observed in E. coli. For example, RAD51, found in yeast, performs the same functions as RecA, i.e., repairing double stranded breaks. 

---