Bj. Rao et Cm. Radding, HOMOLOGOUS RECOGNITION PROMOTED BY RECA PROTEIN VIA NON-WATSON-CRICK BONDS BETWEEN IDENTICAL DNA STRANDS, Proceedings of the National Academy of Sciences of the United Statesof America, 90(14), 1993, pp. 6646-6650
The RecA protein of Escherichia coli forms a nucleoprotein filament th
at promotes homologous recognition and subsequent strand exchange betw
een a single strand and duplex DNA via a three-stranded intermediate.
Recognition of homology within three-stranded nucleoprotein complexes,
which is probably central to genetic recombination, is not well under
stood as compared with the mutual recognition of complementary single
strands by Watson-Crick base pairing. Using oligonucleotides, we exami
ned the determinants of homologous recognition within RecA nucleoprote
in filaments. Filaments that contained a single strand of DNA recogniz
ed homology not only in a complementary oligonucleotide but also in an
identical oligonucleotide, whether their respective sugar-phosphate b
ackbones were antiparallel or parallel, and a filament that contained
duplex DNA showed the same polymorphic versatility in the recognition
of homology. Recognition of self by a filament that contains a single
strand reveals that RecA filaments can recognize homology via non-Wats
on-Crick hydrogen bonds. Recognition of multiple forms of the same seq
uence by duplex DNA in the filament shows that it primarily senses bas
e-sequence homology, and suggests that recognition can be accomplished
prior to the establishment of new Watson-Crick base pairs in heterodu
plex products. However, unlike the initial recognition of homology, st
rand exchange is stereospecific, requiring the proper antiparallel ori
entation of complementary strands.