To translate proteins containing the amino acid cysteine, organisms require cysteine-loaded tRNAs. Most organisms make these by attaching premade cysteine to the tRNA. Sll's team has now revealed that some members of the class of microbes known as archaea take a different path: They first attach a precursor amino acid to the tRNA, then convert it to cysteine (Science 2005, 307, 1969). The new path is chemically analogous to the one organisms use to make the selenocysteine-loaded tRNAs required to insert selenocysteine, the 21st amino acid, into proteins, Sll points out. The archaea Sll studied use a ligase enzyme (SepRS) to make tRNA-bound O-phosphoserine and then use a second enzyme (SepCysS) to convert the tRNA-bound amino acid to cysteine.
by Amanda Yarnell |
March 28, 2005