Palm L, Andersen J, Rahbek-Nielsen H, Hansen T S, Kristiansen K, Højrup P
Department of Molecular Biology, Odense University, Denmark.
J Biol Chem. 1995 Mar 17;270(11):6000-5. doi: 10.1074/jbc.270.11.6000.
A single basic ribosomal protein, protein S7, can be multiply phosphorylated in the ciliated protozoan Tetrahymena. Induction of phosphorylation is highly regulated, and the phosphorylation proceeds in a strictly sequential manner. The first site to be phosphorylated is a serine residue and the second a threonine. In this paper we report the complete primary structure of Tetrahymena thermophila ribosomal protein S7 including identification of the phosphorylated serine and threonine residues. Most of the sequence information was obtained from peptides generated by in situ digestion of S7 in two-dimensional gels using an approach that combined traditional protein chemistry with mass spectrometry. T. thermophila ribosomal protein S7 has a molecular mass of 29,459 Da and contains 259 amino acid residues. Phosphorylation takes place on Ser258 and Thr248 in the C-terminal region of the protein. Alignment of T. thermophila ribosomal protein S7 with known ribosomal proteins yielded the surprising result that T. thermophila S7 is homologous, not with mammalian ribosomal protein S6, but with mammalian ribosomal protein S4. These findings clearly distinguish the pattern of phosphorylation of ribosomal proteins in Tetrahymena from all other eukaryotes analyzed to date.
在纤毛原生动物嗜热栖热菌中，单一的碱性核糖体蛋白S7可发生多次磷酸化。磷酸化的诱导受到高度调控，且磷酸化过程严格按顺序进行。第一个被磷酸化的位点是一个丝氨酸残基，第二个是苏氨酸。在本文中，我们报道了嗜热栖热菌核糖体蛋白S7的完整一级结构，包括对磷酸化丝氨酸和苏氨酸残基的鉴定。大部分序列信息是通过结合传统蛋白质化学和质谱的方法，从二维凝胶中对S7进行原位消化产生的肽段获得的。嗜热栖热菌核糖体蛋白S7的分子量为29459道尔顿，包含259个氨基酸残基。磷酸化发生在该蛋白C端区域的Ser258和Thr248上。将嗜热栖热菌核糖体蛋白S7与已知核糖体蛋白进行比对，得出了一个惊人的结果，即嗜热栖热菌S7与哺乳动物核糖体蛋白S6不同源，而是与哺乳动物核糖体蛋白S4同源。这些发现清楚地将嗜热栖热菌中核糖体蛋白的磷酸化模式与迄今为止分析的所有其他真核生物区分开来。
