A polypeptide (Mr = 15,000) has been purified from Escherichia coli cell extracts that significantly stimulates the duplex DNA unwinding reaction catalyzed by E. coli Rep protein. The Rep helicase unwinding reaction was stimulated by as much as 20-fold, upon addition of the stimulatory protein, using either a 71-base pair or a 343-base pair partial duplex DNA molecule as a substrate. The purifi...

The yeast Srs2 helicase removes Rad51 nucleoprotein filaments from single-stranded DNA (ssDNA), preventing DNA strand invasion and exchange by homologous recombination. This activity requires a physical interaction between Srs2 and Rad51, which stimulates ATP turnover in the Rad51 nucleoprotein filament and causes dissociation of Rad51 from ssDNA. Srs2 also possesses a DNA unwinding activity an...

Bloom syndrome (BS) is a rare genetic disorder characterized by genomic instability and a high predisposition to cancer. The gene defective in BS, BLM, encodes a member of the RecQ family of 3'-5' DNA helicases, and is proposed to function in recombinational repair during DNA replication. Here, we have utilized single-molecule fluorescence resonance energy transfer microscopy to examine the beh...

A new DNA precipitation assay used together with the alkali unwinding assay may provide a rapid means of detecting DNA damage in addition to strand breaks based on the relative amount of damage measured by the two assays. X-rays, Adriamycin, 4-nitroquinoline-N-oxide, N-methyl-N'-nitrosoguanidine, bleomycin, RSU 1172, and five other drugs produced the same relative amount of strand breakage by u...

The helicase and primase activities of the hexameric ring-shaped T7 gp4 protein reside in two separate domains connected by a linker region. This linker region is part of the subunit interface between monomers, and point mutations in this region have deleterious effects on the helicase functions. One such linker region mutant, A257T, is analogous to the A359T mutant of the homologous human mito...

Mutant, but not wild-type p53 binds with high affinity to a variety of MAR-DNA elements (MARs), suggesting that MAR-binding of mutant p53 relates to the dominant-oncogenic activities proposed for mutant p53. MARs recognized by mutant p53 share AT richness and contain variations of an AATATATTT "DNA-unwinding motif," which enhances the structural dynamics of chromatin and promotes regional DNA b...

Helicases that both unwind and rewind DNA have central roles in DNA repair and genetic recombination. In contrast to unwinding, DNA rewinding by helicases has proved difficult to characterize biochemically because of its thermodynamically downhill nature. Here we use single-molecule assays to mechanically destabilize a DNA molecule and follow, in real time, unwinding and rewinding by two DNA re...

The origin (ori)-binding protein of herpes simplex virus type 1 (HSV-1), encoded by the UL9 open reading frame, has been shown to physically interact with a number of cellular and viral proteins, including three HSV-1 proteins (ICP8, UL42, and UL8) essential for ori-dependent DNA replication. In this report, it is demonstrated for the first time that the DNA polymerase processivity factor, UL42...

DNA helicases are motor proteins that catalyze the unwinding of double-stranded DNA into single-stranded DNA using the free energy from ATP hydrolysis. Single molecule approaches enable us to address detailed mechanistic questions about how such enzymes move processively along DNA. Here, an optical method has been developed to follow the unwinding of multiple DNA molecules simultaneously in rea...