Real time fluorescence analysis of the RecA filament: implications of base pair fluidity in repeat realignment

FEBS Letters

Krishnamoorthy, G²  Rao, Basuthkar J¹  Sen, Subhojit¹ 

[1] Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Rd., Colaba, Bombay 400005, India;Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Rd., Colaba, Bombay 400005, India

关键词: RecA;    DNA repeat;    Realignment;    2-Aminopurine;    Cross talk;    ATP;    adenosine triphosphate;    ATPγS;    adenosine 5′-O-(3-thiotriphosphate);    2AP;    2-aminopurine;    BSA;    bovine serum albumin;    dsDNA;    double stranded DNA;    DNase I;    deoxyribonuclease I;    DTT;    dithiothreitol;    EDTA;    ethylenediaminetetraacetic acid;    SDS;    sodium dodecyl sulfate;    SSB;    single stranded DNA binding protein;    ssDNA;    single stranded DNA;   

DOI  :  10.1016/S0014-5793(01)02215-3

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

During recombination, when Escherichia coli RecA mediates annealing across DNA repeats, Watson–Crick chemistry can only specify the complementarity of pairing, but not the most optimal frame of alignment. We describe that although stochastic alignments across poly(dA) and poly(dT) can lead to sub-optimally annealed duplexes containing ssDNA gaps/overhangs, the same are realigned into an optimal frame by a putative motor activity of RecA [Sen et al. (2000) Biochemistry 39, 10196–10206]. In the present study, we analyze the nature of realignment intermediates in real time, by employing a fluorescent probe, 2-aminopurine (2AP), which can not only report the status of RecA on the unstacked duplex, but also the fluidity of bases in such a filament. Although known to display a lower affinity for duplex DNA, RecA seems to remain functionally associated with these sub-optimally aligned repeat duplexes, until the realignment approaches completion. Moreover, a comparison of 2AP fluorescence in repeat versus mixed sequences indicates that bases in a RecA repetitive DNA filament exhibit higher degrees of freedom that might mediate a ‘non-planar hydrogen bonding cross talk’ across the bases on either strand. We discuss a model to explain the mechanistic basis of realignment and its implications in signaling the end of homology maximization, which triggers RecA fall off.

【 授权许可】

Unknown