PubMed Health⌕ Search

Biomedical subjects

S K Neuendorf

Publications and source records attributed to S K Neuendorf.

8 recordsLinked to original sources
PubMed1987

recA protein-promoted ATP hydrolysis occurs throughout recA nucleoprotein filaments.

When recA protein binds cooperatively to single-stranded DNA to form filamentous nucleoprotein complexes, it becomes competent to hydrolyze ATP. No correlation exists between the ends of such complexes and the rate of ATP hydrolysis. ATP hydrolysis is not, therefore, restricted to the terminal subunits on cooperatively bound recA oligomers, but occurs throughout the complex. Similarly, during recA protein-promoted branch migration (during DNA strand exchange), ATP hydrolysis is not restricted to recA protein monomers at the branch point. DNA cofactors of lengths varying from 16 bases to over 12,000 bases support ATP hydrolysis. The maximum value of kcat at infinite DNA concentration is about 29/min independent of the length of the DNA cofactor. The apparent dissociation constant, however, is a strong function of DNA length, providing evidence for a minimum site size of 30-50 bases for efficient binding of recA protein.

Adenosine Triphosphatases↗
PubMed1986

Exchange of recA protein between adjacent recA protein-single-stranded DNA complexes.

We have examined the exchange of recA protein between stable complexes formed with single-stranded DNA (ssDNA) and (a) other complexes and (b) a pool of free recA protein. We have also examined the relationship of ATP hydrolysis to these exchange reactions. Exchange was observed between two different recA X ssDNA complexes in the presence of ATP. Complete equilibration between two sets of complexes occurred with a t1/2 of 3-7 min under a set of conditions previously found to be optimal for recA protein-promoted DNA strand exchange. Approximately 200 ATPs were hydrolyzed for every detected migration of a recA monomer from one complex to another. This exchange occurred primarily between adjacent complexes, however. Little or no exchange was observed between recA X ssDNA complexes and the free recA protein pool, even after several hundred molecules of ATP had been hydrolyzed for every recA monomer present. ATP hydrolysis is not coupled to complete dissociation or association of recA protein from or with recA X ssDNA complexes under these conditions.

Adenosine Triphosphate↗
PubMed1984

Unidirectional branch migration promoted by nucleoprotein filaments of RecA protein and DNA.

Described above are the initial results from a series of experiments designed to more carefully define the mechanism of RecA protein-promoted DNA strand exchange, and in particular, the branch migration phase of this reaction. We have also presented two general models for RecA protein-promoted branch migration. Although the data required to demonstrate a particular mechanism are presently unavailable, we believe these models will provide a useful framework to suggest future experiments. The models also suggest possible explanations for observations that are presently unexplained. In particular, it is possible to explain the observed inefficiency of ATP hydrolysis in this system without invoking the notion that much of the ATP hydrolysis observed is simply uncoupled. If the utilization of extensive filaments of RecA protein to carry out branch migration is inherently inefficient, why might such a mechanism be employed by the cell? The answer to this question may lie in the role of RecA protein-promoted branch migration in post-replication repair (West et al. 1981c). It might be expected that the branch points in a RecA protein-promoted branch migration reaction are susceptible to nuclease degradation. Such degradation would halt branch migration and prevent postreplication repair. One of the roles of the RecA nucleoprotein filament may be to protect the branch point from nuclease degradation and ensure formation of an extensive region of heteroduplex DNA. The apparent energetic cost of this reaction may be a relatively small price to pay to ensure the repair of a potentially lethal DNA lesion.

DNA, Bacterial↗