The Ribosome
Ribosomes are ancient molecular machines that are responsible for production
of protein in all living cells. They are large (2.5 MD molecular weight or larger)
macromolecular complexes composed of RNA (2/3) and protein (1/3). Ribosomes read
the nucleotide sequence of a messenger RNA (mRNA) into a protein sequence, using
the genetic code. They use transfer RNAs (tRNAs) to mediate this process of
translation from the nucleotide language of RNA and DNA into the amino acid
language of proteins.
Cells typically contain many thousands of ribosomes.
Each ribosome can bind one mRNA and up to three tRNAs. Each new amino acid is
brought into the ribosome as an aminoacyl-tRNA, by elongation factor EF-Tu.
The nascent protein chain is transferred from a peptidyl-tRNA to the newly
introduced aminoacyl-tRNA in a reaction catalyzed by peptidyl transferase,
an enzymatic activity that is part of the structure of the ribosome.
Elongation factor EF-G catalyzes the movement of tRNA and mRNA through the
ribosome during translation.
In the Noller laboratory, the structure of the complete Thermus thermophilus
70S ribosome was crystallized in a complex containing mRNA and two or three
tRNAs (bound to the A, P and E sites of the ribosome), and solved by x-ray
crystallography to a resolution of 5.5 Å (Cate et al., 1999; Yusupov et al., 2001).
The path of the mRNA through the ribosome was also determined crystallographically
using difference Fourier methods (Yusupova et al., 2001).