Arenson T A, Tsodikov O V, Cox M M
Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
J Mol Biol. 1999 May 7;288(3):391-401. doi: 10.1006/jmbi.1999.2705.
On linear single-stranded DNA, RecA filaments assemble and disassemble in the 5' to 3' direction. Monomers (or other units) associate at one end and dissociate from the other. ATP hydrolysis occurs throughout the filament. Dissociation can result when ATP is hydrolyzed by the monomer at the disassembly end. We have developed a comprehensive model for the end-dependent filament disassembly process. The model accounts not only for disassembly, but also for the limited reassembly that occurs as DNA is vacated by disassembling filaments. The overall process can be monitored quantitatively by following the resulting decline in DNA-dependent ATP hydrolysis. The rate of disassembly is highly pH dependent, being negligible at pH 6 and reaching a maximum at pH values above 7. 5. The rate of disassembly is not significantly affected by the concentration of free RecA protein within the experimental uncertainty. For filaments on single-stranded DNA, the monomer kcat for ATP hydrolysis is 30 min-1, and disassembly proceeds at a maximum rate of 60-70 monomers per minute per filament end. The latter rate is that predicted if the ATP hydrolytic cycles of adjacent monomers are not coupled in any way.
在线性单链DNA上，RecA丝在5'至3'方向上组装和解聚。单体（或其他单元）在一端结合，从另一端解离。整个丝状体都会发生ATP水解。当ATP在解聚端被单体水解时，就会导致解离。我们已经开发出一种用于末端依赖性丝状体解聚过程的综合模型。该模型不仅考虑了解聚，还考虑了随着丝状体解聚使DNA空出时发生的有限的重新组装。通过跟踪由此导致的依赖DNA的ATP水解下降，可以定量监测整个过程。解聚速率高度依赖于pH值，在pH 6时可忽略不计，在pH值高于7.5时达到最大值。在实验误差范围内，解聚速率不受游离RecA蛋白浓度的显著影响。对于单链DNA上的丝状体，ATP水解的单体催化常数为30分钟-1，解聚以每丝端每分钟60 - 70个单体的最大速率进行。如果相邻单体的ATP水解循环不以任何方式耦合，后者就是预测的速率。
