Trapping Human Ribosomal Protein Genes

The Ribosome

The proteins of all cells are assembled by the ribosome, the oldest molecular machine to have evolved in biological systems. Composed, in human cells, of four RNA molecules and 79 proteins, it is unchanged in function and nearly unchanged in structure during the >2 billion years that have passed since the separation of the eubacterial, archaebacterial, and eukaryotic kingdoms. Enormous efforts over the past 40 years have elucidated a strikingly detailed view of the structure and function of theEscherichia coli ribosome (for review, see Wilson and Noller 1998). Because of the basic conservation of the ribosome, it will be possible to extrapolate most of that structural and functional information to the mammalian ribosome.

The abundance of the four rRNA molecules led to an early determination of their sequences (Gonzalez et al. 1985; McCallum and Maden 1985). In contrast, the 79 ribosomal proteins are diverse, often insoluble, and can be identified only on the basis of their association with the ribosome. However, through a tour de force of technology and persistence, J.G. Wool, Y.-L. Chan, and colleagues (1995, and pers. comm.) have recently completed the sequence determination of the complete set of mammalian ribosomal proteins. Comparison with the sequence of the genome of Saccharomyces cerevisiaedemonstrated that there is a close yeast homolog for all but one of the mammalian ribosomal proteins, demonstrating again the conservation of this machine during evolution.