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J Marsault

Publications and source records attributed to J Marsault.

6 recordsLinked to original sources
PubMed2000

Reverse gyrase, the two domains intimately cooperate to promote positive supercoiling.

Reverse gyrases are atypical topoisomerases present in hyperthermophiles and are able to positively supercoil a circular DNA. Despite a number of studies, the mechanism by which they perform this peculiar activity is still unclear. Sequence data suggested that reverse gyrases are composed of two putative domains, a helicase-like and a topoisomerase I, usually in a single polypeptide. Based on these predictions, we have separately expressed the putative domains and the full-length polypeptide of Sulfolobus acidocaldarius reverse gyrase as recombinant proteins in Escherichia coli. We show the following. (i) The full-length recombinant enzyme sustains ATP-dependent positive supercoiling as efficiently as the wild type reverse gyrase. (ii) The topoisomerase domain exhibits a DNA relaxation activity by itself, although relatively low. (iii) We failed to detect helicase activity for both the N-terminal domain and the full-length reverse gyrase. (iv) Simple mixing of the two domains reconstitutes positive supercoiling activity at 75 degrees C. The cooperation between the domains seems specific, as the topoisomerase domain cannot be replaced by another thermophilic topoisomerase I, and the helicase-like cannot be replaced by a true helicase. (v) The helicase-like domain is not capable of promoting stoichiometric DNA unwinding by itself; like the supercoiling activity, unwinding requires the cooperation of both domains, either separately expressed or in a single polypeptide. However, unwinding occurs in the absence of ATP and DNA cleavage, indicating a structural effect upon binding to DNA. These results suggest that the N-terminal domain does not directly unwind DNA but acts more likely by driving ATP-dependent conformational changes within the whole enzyme, reminiscent of a protein motor.

Adenosine Triphosphate↗
PubMed1994

SAV, an archaebacterial gene with extensive homology to a family of highly conserved eukaryotic ATPases.

Nucleotide sequencing of a region of the hyperthermophilic archaebacterium Sulfolobus acidocaldarius allowed us to identify an open reading frame of 780 amino acids strikingly similar to a family of eukaryotic ATPases, involved in a variety of biological functions. Sequence analysis of the predicted polypeptide revealed 63 to 66% similarity with S. cerevisiae CDC 48p and its related genes in amphibians (p97ATPase) and mammals (Valosin Containing Protein, VCP), all possibly involved in the regulation of the cell cycle. The finding of an archaebacterial equivalent of these proteins with a high degree of similarity suggests that it represents the same gene in these various species. The new archaebacterial ORF, called SAV (S. acidocaldarius VCP-like) exhibited the usual signature of all members of the family, a highly conserved domain of about 200 amino acids, which is duplicated. Thus, apart from the VCP-like proteins, SAV also appeared similar, although less clearly, to other ATPases, members of the family, involved in vesicle-mediated transport (NSF, Sec18p), peroxysome assembly (PAS1p), and gene expression in yeast (SUG1p) and in human immunodeficiency virus (TBP-1). Finally, the discovery of the archaebacterial gene could enlighten not only the evolutionary relationships between the members of this complex ATPase family, but also the cellular function of these proteins, that is presently obscure.

ATPases Associated with Diverse Cellular Activitie↗
PubMed1988

Effects of the Xenopus laevis mitochondrial single-stranded DNA-binding protein on the activity of DNA polymerase gamma.

The single-stranded DNA-binding protein from Xenopus laevis oocyte mitochondria, which has been found associated with the D loop, binds to ssDNA in stoichiometric amounts and can under certain conditions stimulate the activity of the DNA polymerase gamma. Its properties suggest that it is involved in strand displacement during the replication of the mitochondrial genome.

Animals↗
PubMed1983

Mitochondrial DNA-binding proteins that bind preferentially to supercoiled molecules containing the D-loop region of Xenopus laevis mtDNA.

From the bulk of the Xenopus laevis mitochondrial proteins insoluble in 1% Triton X-100 + 1M NaCl, we have isolated, by DNA-cellulose chromatography, a protein fraction enriched in DNA-binding proteins. This fraction contains proteins showing a specific affinity for supercoiled DNA molecules containing the mitochondrial DNA displacement-loop region, as measured by filter binding and competition assays.

Animals↗