STARVATION, MUTATION RATES, AND THE STRINGENT RESPONSE

据估计，DNA损伤最终导致了80%到90%的 人类癌症。这项研究的长期目标是了解 突变率、DNA修复、转录、 饥饿和四磷酸鸟苷(PpGpp)的积累。这个 正在研究的模型系统是E.ColiK12，并且突变率 分析了氨基酸营养缺陷菌向原生营养的逆转。这个 两种不同基因的大肠杆菌K12营养缺陷菌的复原率 在没有丝氨酸或存在丝氨酸的情况下测定了Rel A 异羟甲酸酯，这会引起严格的反应。LEU的复原率 B-和Arg H-在RelA+中均显著高于Rel A+ Rel A-株，两株Leu B-的反转率均为 丝氨酸异羟甲酸酯的存在增强了它的稳定性。正相关关系有 也建立了恢复率和累积的 在丝氨酸异羟甲酸酯存在和不存在的情况下，ppGpp。特定的 未来调查的目标是： 1.确定复原率的依赖关系和累积 等基因菌株中的ppGpp： (A)ppGpp降解，受ppGpp 3‘焦磷水解酶控制 由SPO-T基因编码； (B)依赖于REC的同源重组函数 ABC基因产物； (C)SOS突变体活性，由rec A、lex A和umu DC控制 基因。 (D)转录修复偶联因子，由mfd基因编码。 2.确定我们的结果的一般性和特殊性 等基因营养缺乏症，通过： (A)引入一种已知在电镀后发生逆转的突变基因 (“适应性突变”)进入同基因菌株，以便测量两者 Rel A+和Rel A-菌株的生长和培养后复发率； (B)测量Ara-、Xyl-或的回复速率和ppGpp累积 GAL突变基因，这是也存在于等基因中的标记 Rel A+和Rel A-菌株，在饥饿期间 碳水化合物。在两个菌株中测量Leu B-恢复率 碳水化合物饥饿。 (C)测量其转录未被转录的基因的突变率 受到严厉回应的刺激。 3.测定Rel A+和Rel A-中Leu B-基因的序列 菌株和这些菌株及其转导子的回复突变体中。

It is estimated that DNA damage ultimately causes 80 to 90 percent of all human cancers. The long-term objective of this research is to understand the relationships between mutation rates, DNA repair, transcription, starvation, and the accumulation of guanosine tetraphosphate (ppGpp). The model system under investigation is E. coli K12, and the mutation rates analyzed are reversions of amino acid auxotrophs to prototrophy. The reversion rates of two isogenic E. coli K12 auxotrophs differing only in rel A have been determined in the absence or presence of serine hydroxamate, which provokes the stringent response. Reversion rates of leu B- and arg H- are both significantly higher in the rel A+ compared to the rel A- strain, and the reversion rate of leu B- in both strains is enhanced by the presence of serine hydroxamate. A positive correlation has also been established between reversion rates and the accumulation of ppGpp in the absence and presence of serine hydroxamate. Specific objectives for future investigations are: 1. To determine the dependance of reversion rates and the accumulation of ppGpp in the isogenic strains on: (a) ppGpp degradation, controlled by ppGpp 3' pyrophosphohydrolase which is encoded by the spo T gene; (b) Homologous recombination functions which are dependant upon the rec ABC gene products; (c) SOS mutator activity, controlled by the rec A, lex A, and umu DC genes. (d) The transcription-repair coupling factor, encoded by the mfd gene. 2. To determine the generality and the specificity of our results with the isogenic auxotrophs by: (a)Introducing a mutant gene known to undergo post-plating reversions ("adaptive mutations") into the isogenic strains, in order to measure both growth and post-plating reversion rates in the rel A+ and rel A-strains; (b) Measuring reversion rates and ppGpp accumulation of the ara-, xyl- or gal- mutant genes, which are markers that are also present in the isogenic rel A+ and rel A- strains, during starvation for amino acids or carbohydrates. Measure leu B- reversion rates in both strains during carbohydrate starvation. (c) Measure mutation rates of a gene the transcription of which is not stimulated by the stringent response. 3. To determine the sequence the leu B- gene in the rel A+ and rel A- strains and in revertants of these strains and their transductants.