Ribosome Protein Heterogeneity: The basis of wide spread roles for specialized ribosomes in tuning global gene expression.

核糖体的传统观点是，每个大小核糖体亚基都由其核糖体RNA和一组确定的核糖体蛋白组成。现在，新出现的证据开始挑战这种静态通用核糖体结构的观点，因为越来越明显的是，不同的核糖体在许多核心核糖体蛋白的组成上可能会有所不同。最近发表的数据也揭示了核糖体不同核糖体蛋白组成的功能含义，因为有例子表明特定核糖体蛋白对特定mRNAs的翻译是必需的。例如，最近发表的工作描述了在发育过程中，特定细胞中特定HOX基因的翻译如何需要含有Rpl38的核糖体。人们可以想象许多场景，如何调整核心核糖体蛋白质含量不同的专门核糖体，以在不同的细胞类型和组织中实现最佳的基因表达。初步数据：在先前发表的量化不同小鼠组织之间某些核糖体蛋白mRNAs差异的数据之后，我们定量比较了一些小鼠组织和细胞系中纯化的核糖体的核糖体蛋白质组。我们的初步数据与mRNA表达数据是一致的，在这些数据中，我们还量化了几种核糖体蛋白的高度可变的丰度，而其他的保持不变。核糖体蛋白质亚群的这种变异性值得进一步研究基因表达的功能含义。为了进一步研究核糖体的变异性，我们追求以下特定目标：目的1)量化核糖体变异：完成对从不同组织和细胞系纯化的核糖体核糖体蛋白质组差异的量化。目的2)核糖体变异体的功能研究：在存在和不存在核糖体蛋白的情况下，鉴定在小鼠3T3细胞系多聚体中活跃翻译的mRNAs。目的3)翻译逃避的机制研究：研究核糖体特异性选择性翻译下的这些mRNAs如何不被规范的5‘-帽依赖翻译所翻译，而需要特定的核糖体蛋白进行翻译的分子基础。影响：通过选择性mRNA翻译来证明核糖体在基因表达中的广泛作用将重新定义我们如何看待核糖体在蛋白质合成中的作用。核糖体的鉴定在基因表达的调控中起着积极的作用，可能是转录后基因调控中最大的被忽视的方面之一，并有可能在发育和疾病中发挥多种调控作用。

The traditional view of the ribosome is where each large and small ribosomal subunit is composed of its ribosomal RNAs and a defined set of ribosomal proteins. Now emerging evidence is beginning to challenge this view of a static universal ribosome structure as it is becoming apparent that different ribosomes can vary in their make-up of many core ribosomal proteins. Recent published data is also revealing the functional implications of variable ribosomal protein composition of ribosomes as there are examples demonstrating the requirement for specific ribosomal proteins for the translation of specific mRNAs. For example, recently published work describes how ribosomes containing Rpl38 are required for the translation of specific Hox genes in specific cells during development. One can envision numerous scenarios how specialized ribosomes which vary in their core ribosomal protein content are tuned for optimal gene expression in different cell types and tissues. Preliminary Data: Following up on previously published data that quantified large differences for some ribosomal protein mRNAs between different murine tissues, we have quantitatively compared the ribosomal proteome of purified ribosomes from some murine tissues and cell lines. Our preliminary data is in agreement with the mRNA expression data where we have also quantified highly variable abundances for several ribosomal proteins while others remain constant. This variability of a subset of ribosomal proteins merits further investigations into the functional implications in gene expression.To further investigate ribosome variability we are pursuing the following Specific Aims:Aim 1) Quantifying Ribosomal Variations: Complete our quantification of the differences in the ribosomal proteome of ribosomes purified from different murine tissues and cell lines. Aim 2) Functional Investigations of Ribosomal Variants: Identify the mRNAs being actively translated in polysomes in the murine 3T3 cell line in the presence and absence of ribosomal proteins that exhibit variable ribosomal occupancy. Aim 3) Mechanistic Investigations of Translational Evasion: Investigate the molecular basis of how these mRNAs under ribosomal specific selective translation are not translated by canonical 5'-cap dependent translation and require specific ribosomal proteins for translation.Impact: The demonstration of the breadth of the role for ribosomes in gene expression by selective mRNA translation would redefine how we view the role of ribosomes in protein synthesis. The identification of ribosomes playing an active role in the regulation of gene expression may be one of the largest overlooked aspects of post transcriptional gene regulation and has the potential to function in numerous regulatory roles in both development and disease.