Xia Bing, Ke Haiping, Jiang Wei, Inouye Masayori
Department of Biochemistry, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
J Biol Chem. 2002 Feb 22;277(8):6005-11. doi: 10.1074/jbc.M109700200. Epub 2001 Dec 12.
The 5'-end region of cspA mRNA contains a Cold Box sequence conserved among several cold-shock mRNAs. This region forms a stable stem-loop structure followed by an AU-rich sequence. Here we show that the Cold Box region is essential for the normal scale of cspA mRNA induction after cold shock because a deletion of the stem-loop significantly destabilizes the mRNA and reduces the cold shock-induced cspA mRNA amount by approximately 50%. The AU-rich track, however, slightly destabilizes the mRNA. The integrity of the stem is essential for the stabilizing function, whereas that of the loop sequence is less important. Overexpression of a mutant cspA mRNA devoid of both the AUG initiation codon and the coding sequence results in a severe growth inhibition at low temperature along with a derepression of the chromosomal cspA expression. Furthermore, the overexpressed RNA is stably associated with the 30 S and 70 S ribosomes. Our results demonstrate that the AUG initiation codon and the coding region containing the downstream box are not required for cspA mRNA to bind ribosomes and that the 5'-untranslated region by itself has a remarkable affinity to ribosomes at low temperature.
cspA mRNA的5'端区域包含一个在几种冷休克mRNA中保守的冷框序列。该区域形成一个稳定的茎环结构，其后是富含AU的序列。我们在此表明，冷框区域对于冷休克后cspA mRNA诱导的正常规模至关重要，因为茎环的缺失会显著使mRNA不稳定，并使冷休克诱导的cspA mRNA量减少约50%。然而，富含AU的序列会使mRNA略有不稳定。茎的完整性对于稳定功能至关重要，而环序列的完整性则不太重要。缺失AUG起始密码子和编码序列的突变cspA mRNA的过表达会导致在低温下严重的生长抑制，同时染色体cspA表达去阻遏。此外，过表达的RNA与30 S和70 S核糖体稳定结合。我们的结果表明，cspA mRNA与核糖体结合不需要AUG起始密码子和包含下游框的编码区域，并且5'非翻译区自身在低温下对核糖体具有显著的亲和力。
