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Variation at the start

Some organisms adopt an unusual strategy to make sure the genetic code is translated accurately, according to study that will be published tomorrow in linkurl:__Molecular Cell.__;http://www.molecule.org/ These findings suggest that ancient organisms may have used different techniques to maintain accuracy in translation before settling on the predominant strategy. In most organisms, the start of translation is coded by the sequence AUG. This sequence triggers the binding of tRNA that carries t

By | February 14, 2008

Some organisms adopt an unusual strategy to make sure the genetic code is translated accurately, according to study that will be published tomorrow in linkurl:__Molecular Cell.__;http://www.molecule.org/ These findings suggest that ancient organisms may have used different techniques to maintain accuracy in translation before settling on the predominant strategy. In most organisms, the start of translation is coded by the sequence AUG. This sequence triggers the binding of tRNA that carries the amino acid methionine. Unfortunately, AUG resembles another code for a different amino acid: AUA, which codes for isoleucine. This subtle difference in the third -- or "wobble" -- position means that there's room for error. In most organisms, to avoid mistaking AUG for AUA, a chemical modification is added to the third position of the isoleucine tRNA. This modification tells the enzyme ARS that it should attach the isoleucine amino acid to the tRNA. Without the modification, ARS will attach methionine, mistakenly initiating translation. But the study by Thomas Jones at Barcelona Institute for Research in Biomedicine and colleagues shows that this isn't the modus operandi for __Mycoplasma penetrans,__ the organism implicated in disease progression for patients with HIV. This organism's ARS doesn't distinguish between methionine and isoleucine using a chemical modification in the tRNA anticodon's wobble position. Instead, the organism's ARS identifies a sequence on the stem of the tRNA as a cue that it should attach the appropriate amino acid -- isoleucine. "This enzyme is using a different recognition strategy for finding its tRNA partner," than the anticodon alone, said Rebecca Alexander from Wake Forest University who is an author on the paper. Even though the __Mycoplasma's__ ARS doesn't require a modification in the wobble for attaching the right amino acid, that change is still important to appropriate translation. The investigators stumbled across differences in tRNA modification while looking for differences in the ARS enzyme that modified tRNA in __Mycoplasma penetrans.__ They reported finding differences in this enzyme's genes, but also found unusual pattern in the tRNA sequence that they investigated further. If the difference in the __Mycosplasma__ ARS proves to be significant enough to differentiate it from human ARS, it could become a target for drug to treat __Mycoplasma__ in HIV patients.
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