EF-1A Mutants Increase Programmed +1 Frameshifting
Frameshift suppressors can arise by mutation of other components of the translational machinery: rRNA, ribosomal proteins or elongation factors. We have recently begun to look at how error-promoting or error-diminishing mutants of the translational machinery affect programmed +1 frameshifting in yeast.
Our most complete work concerns the frameshift suppressing alleles of the gene encoding elongation factor-1A (EF-1A, formerly known as EF-Tu in bacteria and EF-1a in eukaryotes). This factor delivers aminoacyl-tRNA to the ribosomal A site. Sandbaken & Culbertson identified many suppressors forms of the TEF2 gene encoding eEF-1A in yeast while Hughes et al. and Vijgenboom et al. identified suppressor forms of bacterial EF-1A. The mutations suppressed both nonsense and frameshift mutations suggesting a general role in translational fidelity. Some of residues altered affected the portion of the factor similar to the small G-protein ras implying that they might alter the GTPase activity that modulates accuracy. Others affected the other two domains of the protein, which interact directly with the aminoacyl-tRNA or ribosome.
We studied the two strongest alleles of TEF2 finding that they strongly stimulated programmed +1 frameshifting. Dinman and Kinzy had similar results and suggested that the eEF-1A mutants might increase ribosomal pausing at frameshift sites. We found evidence suggesting that the mutants do not affect pausing but rather that they alter the fidelity of aminoacyl-tRNA recruitment (Vimaladithan and Farabaugh). We are continuing to study the interaction between eEF-1A, tRNAs and the ribosome to determine how accuracy is disruptd.