Avni D, Biberman Y, Meyuhas O
Department of Biochemistry, The Hebrew University Hadassah Medical School, PO Box 12272, Jerusalem 91120, Israel.
Nucleic Acids Res. 1997 Mar 1;25(5):995-1001. doi: 10.1093/nar/25.5.995.
TOP mRNAs are vertebrate transcripts which contain a 5'terminal oligopyrimidine tract (5'TOP), encode for ribosomal proteins and elongation factors 1alpha and 2, and are candidates for growth-dependent translational control mediated through their 5'TOP. In the present study we show that elongation factor 2 (EF2) mRNA is translationally regulated in a growth-dependent manner in cells of hematopoietic origin, but not in any of three different non-hematopoietic cell lines studied. Human beta1-tubulin mRNA is a new member of the family which contains all the hallmarks of a typical TOP mRNA, yet its translation is refractory to growth arrest of any of the examined cell lines. Transfection experiments indicate that the first 29 and 53 nucleotides of the mRNAs encoding EF2 and beta1-tubulin, respectively, contain all the translational cis-regulatory elements sufficient for ubiquitously conferring growth-dependent translational control on a reporter mRNA. These results suggest that the distinct translational regulation of TOP mRNAs reflects downstream sequences which can override the regulatory features of the 5'TOP in a cell type-specific manner. This notion is further supported by the fact that mutations within the region immediately downstream of the 5'TOP of rpS16 mRNA confer onto the resulting transcripts growth-dependent translational control with a cell type specificity similar to that displayed by EF2 mRNA.
TOP mRNA是脊椎动物转录本，其含有5'端寡嘧啶序列（5'TOP），编码核糖体蛋白以及延伸因子1α和2，并且是通过其5'TOP介导的生长依赖性翻译控制的候选对象。在本研究中，我们发现延伸因子2（EF2）mRNA在造血来源的细胞中以生长依赖性方式受到翻译调控，但在所研究的三种不同的非造血细胞系中均未观察到这种现象。人β1-微管蛋白mRNA是该家族的新成员，具有典型TOP mRNA的所有特征，但其翻译对任何受试细胞系的生长停滞均不敏感。转染实验表明，分别编码EF2和β1-微管蛋白的mRNA的前29和53个核苷酸包含所有翻译顺式调控元件，足以将生长依赖性翻译控制普遍赋予报告基因mRNA。这些结果表明，TOP mRNA独特的翻译调控反映了下游序列，这些序列可以以细胞类型特异性方式超越5'TOP的调控特征。rpS16 mRNA的5'TOP紧邻区域内的突变赋予所得转录本生长依赖性翻译控制，其细胞类型特异性与EF2 mRNA相似，这一事实进一步支持了这一观点。
