Ackerman said that when the team began its studies, it did not expect that such a fundamental defect in protein synthesis could be behind the neurodegeneration they had observed in sticky mice. "There were a lot of candidate genes in the chromosomal region containing the sti mutation," she said, "and this gene was actually the last candidate gene we investigated. It seemed to us that a mutation in a gene so fundamentally important for protein translation would cause early lethality. But when we couldn't find a defect in any of the other genes in the sti region, we decided to look closer at the tRNA synthetase gene. And there it was."
To set aside any doubts they might have had about the role of the tRNA synthetase gene, Ackerman and her colleagues showed that they could correct the pathology in the sticky mouse mutants by using genetic techniques to insert a normal version of the tRNA synthetase gene.
To understand the specific defect in the tRNA synthetase gene, Ackerman and her colleagues collaborated with Schimmel, whose research has concentrated on the biochemistry of synthetases. Molecular studies by Schimmel and his colleagues revealed that the defect in the sti mutant mouse occurred in a region of the synthetase enzyme that "edits" the loading of the correct amino acid, alanine, onto its carrier tRNA. This editing enables the enzyme to reject incorrect amino acids.
The researchers found that the mutant enzyme would ch
Source:Howard Hughes Medical Institute