Authentic precursors to ribosomal subunits accumulate in Escherichia coli in the absence of functional DnaK chaperone
Authentic precursors to ribosomal subunits accumulate in Escherichia coli in the absence of functional DnaK chaperone
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DOI：
10.1046/j.1365-2958.2003.03813.x
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发表时间：
2004-01-01
影响因子：
3.6
通讯作者：
Alix, JH
中科院分区：
文献类型：
--
作者：
Hage, AE;Alix, JH
大肠杆菌dnaK-ts突变体在高温下核糖体生物合成的后期阶段有缺陷。在这里，我们表明，在dnaK 756-ts突变体中积累的21 S，32 S和45 S核糖体颗粒在44 ℃下含有未加工形式的16 S和23 S rRNA（在45 S颗粒的情况下部分加工）。它们的5S rRNA化学计量和核糖体蛋白组成是在野生型（dnaK（+））菌株中发现的典型的真正核糖体前体。尽管缺乏功能性DnaK，但这些21 S、32 S和45 S颗粒在高温下仍然非常缓慢地成熟为结构和功能正常的30 S和50 S核糖体亚基。这种转化伴随着p16 S和p23 S rRNA向其成熟形式的加工。我们的结论是：（i）21 S、32 S和45 S颗粒不是死端颗粒，而是活性核糖体的真正前体（21 S颗粒转化为30 S亚基，32 S和45 S转化为50 S亚基）;（ii）DnaK不是核糖体生物合成所必需的，但在高温下大大加速了这一过程的后期步骤;和（iii）23 S rRNA加工依赖于50 S亚基逐步组装所达到的阶段，而不是直接依赖于DnaK。
Escherichia coli dnaK-ts mutants are defective in the late stages of ribosome biogenesis at high temperature. Here, we show that the 21S, 32S and 45S ribosomal particles that accumulate in the dnaK756-ts mutant at 44degreesC contain unprocessed forms of their 16S and 23S rRNAs (partially processed in the case of 45S particles). Their 5S rRNA stoichiometry and ribosomal protein composition are typical of the genuine ribosomal precursors found in a wild-type (dnaK(+)) strain. Despite the lack of a functional DnaK, a very slow maturation of these 21S, 32S and 45S particles to structurally and functionally normal 30S and 50S ribosomal subunits still occurs at high temperature. This conversion is accompanied by the processing of p16S and p23S rRNAs to their mature forms. We conclude that: (i) 21S, 32S and 45S particles are not dead-end particles, but true precursors to active ribosomes (21S particles are converted to 30S subunits, and 32S and 45S to 50S subunits); (ii) DnaK is not absolutely necessary for ribosome biogenesis, but accelerates the late steps of this process considerably at high temperature; and (iii) 23S rRNA processing depends on the stage reached in the stepwise assembly of the 50S subunit, not directly on DnaK.