Coutts M, Krowczynska A, Brawerman G
Department of Biochemistry, Tufts University Health Sciences Schools, Boston, MA 02111.
Biochim Biophys Acta. 1993 Apr 29;1173(1):49-56. doi: 10.1016/0167-4781(93)90241-5.
The mRNA present in extracts of mouse sarcoma 180 (S-180) ascites cells is relatively resistant to degradation when compared to added tracer ribosomal RNA. Deproteinized mRNA added to the extract is about as resistant as the endogenous mRNA, an indication that the protection is not due to any protein present in the endogenous mRNP structure. A major determinant of protection lies at the 5' end of RNA chains, where the presence of a triphosphate or a cap enhances the stability of mRNA transcripts. Addition of poly(A) to a capped transcript had little effect on stability. Stabilization by the cap structure is apparently not due to association of transcripts with a cap-binding protein. The discrimination in RNA decay rates appears to be based on interaction of the different RNA species with an exonuclease, which represents the predominant ribonuclease activity in the extract. Other major cytoplasmic nucleases are suppressed by an RNase inhibitor that is present in excess.
与添加的示踪核糖体RNA相比，小鼠肉瘤180（S-180）腹水细胞提取物中存在的mRNA对降解相对具有抗性。添加到提取物中的脱蛋白mRNA与内源性mRNA的抗性相当，这表明这种保护作用并非由于内源性mRNP结构中存在的任何蛋白质。保护作用的一个主要决定因素位于RNA链的5'端，三磷酸或帽结构的存在可增强mRNA转录本的稳定性。向加帽转录本中添加聚（A）对稳定性影响不大。帽结构介导的稳定性增强显然不是由于转录本与帽结合蛋白的结合。RNA衰变率的差异似乎基于不同RNA种类与外切核酸酶的相互作用，外切核酸酶是提取物中主要的核糖核酸酶活性成分。其他主要的细胞质核酸酶被过量存在的核糖核酸酶抑制剂所抑制。
