Small, Acid-Soluble Spore Proteins of the α/β Type Do Not Protect the DNA in Bacillus subtilis Spores against Base Alkylation

Ethyl methanesulfonate (EMS) killed wild-type Bacillus subtilis spores as rapidly as spores lacking small, acid-soluble proteins (SASP) of the α/β type (α(−)β(−) spores), and 20% of the survivors had obvious mutations. A recA mutation increased the EMS sensitivity of wild-type and α(−)β(−) spores similarly but reduced their mutagenesis; EMS treatment of dormant spores also resulted in the induction of RecA synthesis during spore germination. EMS generated similar levels of alkylated bases in wild-type and α(−)β(−) spore DNAs, in purified DNA, or in DNA saturated with α/β-type SASP. Ethylene oxide (EtO) also generated similar levels of base alkylation in wild-type and α(−)β(−) spore DNAs. These data indicate that EMS and EtO kill spores at least in part by DNA damage but that α/β-type SASP, which protect DNA against many types of damage, do not protect spore DNA from base alkylation.

甲磺酸乙酯（Ethyl methanesulfonate, EMS）对野生型枯草芽孢杆菌芽孢的杀伤速率，与缺失α/β型小分子酸溶性蛋白（SASP）的芽孢（α(-)β(-)芽孢）相当，且有20%的存活芽孢出现了明显突变。recA基因突变可同等提升野生型与α(-)β(-)芽孢对EMS的敏感性，但会降低二者的诱变效应；对休眠芽孢施以EMS处理，还可诱导芽孢萌发过程中RecA蛋白的合成。EMS可在野生型与α(-)β(-)芽孢的DNA、纯化DNA，或是结合α/β型SASP饱和的DNA中，诱导产生水平相近的烷基化碱基。环氧乙烷（Ethylene oxide, EtO）在野生型与α(-)β(-)芽孢的DNA中，同样可诱导产生水平相近的碱基烷基化产物。上述数据表明，EMS与EtO至少可通过DNA损伤途径杀伤芽孢，但α/β型SASP这类可保护DNA抵御多种类型损伤的蛋白，无法为芽孢DNA提供针对碱基烷基化损伤的保护作用。