A long A+T-rich sequence in supercoiled pBR322 DNA is hypersensitive to single-strand-specific nucleases at 37 degrees C but not at reduced temperature. The basis for the nuclease hypersensitivity is stable DNA unwinding as revealed by (i) the same temperature dependence for hypersensitivity and for stable unwinding of plasmid topoisomers after two-dimensional gel electrophoresis, (ii) preferential nuclease digestion of stably unwound topoisomers, and (iii) quantitative nicking of stably unwound topoisomers in the A+T-rich region. Nuclease hypersensitivity of A+T-rich sequences is hierarchical, and either deletion of the primary site or a sufficient increase in the free energy of supercoiling leads to enhanced nicking at an alternative A+T-rich site. The hierarchy of nuclease hypersensitivity reflects a hierarchy in the free energy required for unwinding naturally occurring sequences in supercoiled DNA. This finding, along with the known hypersensitivity of replication origins and transcriptional regulatory regions, has important implications for using single-strand-specific nucleases in DNA structure-function studies.
Altered DNA conformations detected by mung bean nuclease occur in promoter and terminator regions of supercoiled pBR322 DNA
Changes in site specificity of single-strand-specific endonucleases on supercoiled PM2 DNA with temperature and ionic environment
Mung bean nuclease cleavage of a dA + dT-rich sequence or an inverted repeat sequence in supercoiled PM2 DNA depends on ionic environment
Topoisomerase I from chicken erythrocytes: purification, characterization, and detection by a deoxyribonucleic acid binding assay
Cruciform formation in a negatively supercoiled DNA may be kinetically forbidden under physiological conditions
Identification and annotation of promoter regions in microbial genome sequences on the basis of DNA stability
Does base composition help predispose the complementarity-determining regions of antibodies to hypermutation?
Sites of predicted stress-induced DNA duplex destabilization occur preferentially at regulatory loci
Linker histones affect patterns of digestion of supercoiled plasmids by single-strand-specific nucleases
Analysis of DNA structure and sequence requirements for Pseudomonas aeruginosa MutL endonuclease activity
Immunoassays for carbodiimide modified DNA-detection of unpairing transitions in supercoiled ColE1 DNA
The DNA unwinding element in a yeast replication origin functions independently of easily unwound sequences present elsewhere on a plasmid
T-antigen binding to site I facilitates initiation of SV40 DNA replication but does not affect bidirectionality
Helicobacter pylori oriC--the first bipartite origin of chromosome replication in Gram-negative bacteria
Stress-induced DNA duplex destabilization (SIDD) in the E. coli genome: SIDD sites are closely associated with promoters
Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) contains two functional lytic origins of DNA replication
Susceptibility to superhelically driven DNA duplex destabilization: a highly conserved property of yeast replication origins
Effect of ethidium binding and superhelix density on the apparent supercoiling free energy and torsion constant of pBR322 DNA
Allergy and Asthma
Allergy and asthma are inflammatory disorders that are triggered by the activation of an allergen-specific regulatory t cell. These t cells become activated when allergens are recognized by allergen-presenting cells. Here is the latest research on allergy and asthma.