Saturation mutagenesis of 5S rRNA in Saccharomyces cerevisiae

rRNAs are the central players in the reactions catalyzed by ribosomes, and the individual rRNAs are actively involved in different ribosome functions. Our previous demonstration that yeast 5S rRNA mutants (called mof9) can im pact translational reading frame maintenance showed an unexpected function for this ubiquitous biomolecule. At the time, however, the highly repetitiv e nature of the genes encoding rRNAs precluded more detailed genetic and mo lecular analyses. A new genetic system allows all 5S rRNAs in the cell to b e transcribed from a small, easily manipulated plasmid. The system is also amenable for the study of the other rRNAs, and provides an ideal genetic pl atform for detailed structural and functional studies. Saturation mutagenes is reveals regions of 5S rRNA that are required for cell viability, transla tional accuracy, and virus propagation. Unexpectedly, very few lethal allel es were identified, demonstrating the resilience of this molecule. Superimp osition of genetic phenotypes on a physical map of 5S rRNA reveals the exis tence of phenotypic clusters of mutants, suggesting that specific regions o f 5S rRNA are important for specific functions. Mapping these mutants onto the Haloarcula marismortui large subunit reveals that these clusters occur at important points of physical interaction between 5S rRNA and the differe nt functional centers of the ribosome. Our analyses lead us to propose that one of the major functions of 5S rRNA may be to enhance translational fide lity by acting as a physical transducer of information between all of the d ifferent functional centers of the ribosome.