Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 187

Translation initiation requires a dedicated aa-tRNA, the formylmethionine initiator tRNA (fMet-tRNA^fMet). This unique aa-tRNA has a formyl group attached to the amino group of the methionine (Figure 2.26), making it resemble a peptidyl-tRNA rather than a normal aminoacyl-tRNA because the amino group on the amino acid is blocked. This causes fMet-tRNA^fMet to bind to the P site rather than the A site of the ribosome, which is an important step in initiation, as discussed below, and prevents its use as an elongator tRNA. The initiator fMet-tRNA^fMet is synthesized somewhat differently from the other aminoacyl-tRNAs. This special tRNA uses the aminoacyl-tRNA synthetase of the normal tRNA^Met to attach methionine to the tRNA^fMet. Then, an enzyme called transformylase adds a formyl group to the amino group of the methionine on the tRNA^fMet to form fMet-tRNA^fMet.