Intermediates in Homologous Pairing Promoted by RecA Protein and Correlations of Recombination In Vitro and In Vivo

Abstract

Using the energy of ATP, RecA protein in vitro promotes the homologous pairing of single-stranded or partially single-stranded DNA (ssDNA) with double-stranded DNA (dsDNA), to form joint molecules in which the two components are held together by the hydrogen bonds of paired bases. The path of the reaction is illustrated in Figure 1 (Shibata et al. 1979; Radding et al. 1981). The reaction can be divided into three sequential stages: presynaptic polymerization of RecA protein on ssDNA; synapsis; and postsynaptic strand exchange (for review, see Radding 1982). A variety of substrates can be used to study the RecA reaction (Radding et al. 1980). One useful and well-defined combination of substrates is illustrated in Figure 2 (DasGupta et al. 1980). This pair of substrates consists of a circular single strand, which is isolated directly from the virions of small DNA phages, and linear dsDNA prepared from the...