Ramabhadran T V, Jagger J
Proc Natl Acad Sci U S A. 1976 Jan;73(1):59-63. doi: 10.1073/pnas.73.1.59.
Continuously growing cultures of E. coli B/r were irradiated with a fluence of broad-band near-ultraviolet radiation (315-405 nm) sufficient to cause extensive growth delay and complete cessation of net RNA synthesis. Chloramphenicol treatment was found to stimulate resumption of RNA synthesis, similar to that observed with chloramphenicol treatment after amino-acid starvation. E. coli strains in which amino-acid starvation does not result in cessation of RNA synthesis ("relaxed" or rel- strains) show no cessation of growth and only a slight effect on the rate of growth or of RNA synthesis. These findings show that such near-UV fluences do not inactivate the RNA synthetic machinery but affect the regulation of RNA synthesis, in a manner similat to that produced by amino-acid starvation. Such regulation is believed to be mediated through alterations in concentration of guanosine tetraphosphate (ppGpp), and our estimations of ppGpp after near-UV irradiation are consistent with such an interpretation. These data, combined with earlier published data, strongly suggest that the mechanism of near-UV-induced growth delay in E. coli involves partial inactivation of certain tRNA species, which is interpreted by the cell in a manner similar to that of amino-acid starvation, causing a rise in ppGpp levels, a shut-off of net RNA synthesis, and the induction of a growth delay.
用足以导致广泛生长延迟和净RNA合成完全停止的宽带近紫外辐射（315 - 405纳米）通量照射不断生长的大肠杆菌B/r培养物。发现氯霉素处理能刺激RNA合成的恢复，这与氨基酸饥饿后用氯霉素处理所观察到的情况相似。在氨基酸饥饿不会导致RNA合成停止的大肠杆菌菌株（“松弛型”或rel-菌株）中，没有观察到生长停止，对生长速率或RNA合成速率只有轻微影响。这些发现表明，这种近紫外通量不会使RNA合成机制失活，而是以类似于氨基酸饥饿所产生的方式影响RNA合成的调控。据信这种调控是通过鸟苷四磷酸（ppGpp）浓度的变化介导的，我们对近紫外照射后ppGpp的估计与这种解释一致。这些数据与早期发表的数据相结合，强烈表明大肠杆菌中近紫外诱导生长延迟的机制涉及某些tRNA种类的部分失活，细胞以类似于氨基酸饥饿的方式对其进行解读，导致ppGpp水平升高、净RNA合成停止以及生长延迟的诱导。
