DNA in dormant spores of Bacillus species is in an A‐like conformation

Abstract

SummaryThe DNA in dormant spores of Bacillus species is associated with a/|3-type smaii, acid-soiuble proteins (SASP), which are double-stranded DNA-binding proteins whose amino acid sequence has been highly conserved in evolution. In vitro these proteins bind most strongly to DNA which readily adopts an A-iike conformation, as binding of a/|3-type SASP causes DNA to assume an A-like conformation. As predicted by this conformational change in DNA, binding of a/ptype SASP to relaxed but covalently closed plasmid DNA results in the introduction of a iarge number of negative supercoils. Associated with the conformational change in DNA brought about by oc/^-type SASP binding is a change in its photochemistry such that ultraviolet irradiation does not generate pyrimidine dimers, but rather a thyminyl-thymine adduct termed spore photoproduct (SP). The latter two properties of DNA complexed with o(/|3-type SASP in vitro are similar to those of DNA in dormant spores of Baciiius species in which: (i) plasmid DNA has a much higher number of negative supercoils than plasmid in growing cells; and (ii) ultraviolet irradiation produces SP and no pyrimidine dimers, while only pyrimidine dimers are formed in growing cells. During sporulation these changes in the properties of spore DNA take place in parallel with synthesis of a/ptype SASP, and the magnitude of the changes is greatly reduced in mutants that make low amounts of these proteins. A straightforward interpretation of these data is that DNA in dormant spores of Bacillus species is in an A-like conformation. DNA in an A-like conformation is also present in growing cells with high a/|3-type SASP levels. However, the presence of this A-like DNA is detrimental to cell growth.

Structure of the DNA-SspC Complex: Implications for DNA Packaging, Protection, and Repair in Bacterial Spores

“…Previous circular dichroism and Fourier transform infrared studies implied that binding of DNA to SspC, a characteristic member of the ␣/␤-type SASP family, promotes a conformational transition of DNA molecules from a B form to an A-like structure (19,31). It was proposed that this major conformational modification underlies the ability of ␣/␤-type SASP to protect spore DNA, by substantially modulating DNA photochemistry (19,31).…”

“…It was proposed that this major conformational modification underlies the ability of ␣/␤-type SASP to protect spore DNA, by substantially modulating DNA photochemistry (19,31). It was also suggested that the change in DNA supercoiling detected following the interaction with SspC in vitro (20), as well as by DNA in spores (21), derives from the large alteration in the number of base pairs per helical turn that accompanies B-to-A DNA transition (31).…”

“…It was proposed that this major conformational modification underlies the ability of ␣/␤-type SASP to protect spore DNA, by substantially modulating DNA photochemistry (19,31). It was also suggested that the change in DNA supercoiling detected following the interaction with SspC in vitro (20), as well as by DNA in spores (21), derives from the large alteration in the number of base pairs per helical turn that accompanies B-to-A DNA transition (31). Subsequent electron microscopy studies of DNA-SspC filaments indicated, however, that the length of DNA molecules, and hence the rise per base pair, are not significantly altered upon SspC binding, thus implying that DNA conformational state within the DNA-SspC complex remains similar to the canonical B form (8).…”

Resistance ofBacillusEndospores to Extreme Terrestrial and Extraterrestrial Environments

“…Spore DNA is saturated with a group of unique proteins called ␣/␤-type SASP (184,186,(189)(190)(191). These proteins are synthesized only during sporulation in the developing spore and are degraded beginning early in spore germination.…”

B-DNA Helix Stability in a Solvent-Free Environment

“…In this study, circular dichroism, mass spectrometry, ion mobility, and molecular dynamics calculations were performed on poly d(CG) n duplexes and mixed sequence duplexes from 18 to 30 bp long. For simplicity, the strands were named by their sequence and length so CG18 ϭ d(CG) 9 , CG22 ϭ d(CG) 11 , CG26 ϭ d(CG) 13 , CG30 ϭ d(CG) 15 , Mix18 ϭ dCAGTGAT(CG) 2 …”