RecA protein promotes rapid RNA-DNA hybridization in heterogeneous RNA mixtures

The nucleoprotein filament formed by the RecA protein of Escherichia coli on single-stranded DNA catalyzes the hybridization of RNA transcripts with single-stranded DNA sequences at 37 degrees C, in vitro. RecA protein rapidly promotes hybridization, even when noncomplementary RNA is in a millionfold nucleotide excess over hybridizing RNA, and in a thousandfold nucleotide excess over hybridizing single-stranded DNA. Heterologous double-stranded DNA and RecA-coated noncomplementary single-stranded DNA are also poor competitors of RNA transcripts produced in vitro. Since large excesses of noncomplementary RNA fail to inhibit sharply the hybridization reaction by RecA protein under mild, non-degradative conditions, the reaction may be useful in the identification and isolation of transcripts produced in vivo.