Modulation of the effects of alpha/beta-type small, acid-soluble spore proteins on DNA by the Bacillus subtilis HBsu protein

Date of Completion

January 2002


Biology, Microbiology




HBsu, the Bacillus subtilis homolog of the E. coli HU proteins and the major chromosomal protein in vegetative cells of B. subtilis, is present at similar levels in vegetative cells and spores (5 × 104 monomers/genome). The level of HBsu in spores was unaffected by the presence or absence of the α/β-type small, acid-soluble proteins (SASP) which are the major chromosomal proteins in spores. In developing B. subtilis forespores and in germinating cells of B. megaterium, the HU homolog colocalized with α/β-type SASP on the nucleoid suggesting that HBsu could modulate α/β-type SASP-mediated properties of spore DNA. Indeed, in vitro studies showed that HBsu altered α/β-type SASP protection of pUC19 from DNase digestion, induced negative DNA supercoiling opposing α/β-type SASP-mediated positive supercoiling, and greatly ameliorated the α/β-type SASP-mediated increase in DNA persistence length. However, HBsu did not significantly interfere with the α/β-type SASP-mediated changes in the UV photochemistry of DNA that explain the heightened resistance of spores to UV radiation. This work supports a role for HBsu in modulating the effects of α/β-type SASP on the properties of DNA in the developing and dormant B. subtilis spore. ^