ABSTRACTS:

ARTICLE TITLE: New horizons for RNA catalysis
AUTHOR: Norman R. Pace
JOURNAL: SCIENCE, 256:1402-3 June 5, 1992
ABSTRACT: This review provides an introduction to the topic of RNA catalysis - the building of peptide units into proteins by the RNA, usually occurring within a ribosome. The formation of the peptide bond is essential to all biochemical life. For the past 35 years ribosomes have been studied to uncover their function in the production of proteins. Recently, however, the RNA itself, within the ribosome, has been found to play a central role in this process. The ribosomal RNA (rRNA) may be responsible for the actual peptide bond formation. Before these recent studies it was believed that other proteins (enzymes) were responsible for peptide formation. Until now the rRNA comprising about 65% of the ribosome was believed to provide the mechanical framework upon which other compounds might act.
The realization that the rRNA is the sole mover in this process shifts its importance whenever we consider the origins of life. Only RNA is known to be capable of the chemistry required to duplicate itself. Add to this the ability to catalyze the production of other proteins. Although protein synthesis may seem complex, the only required ingredients are rRNA, tRNA, mRNA and raw amino acids. Viewed this way, RNA is the foundation of cellular life.

KEY WORDS/PHRASES
Enzymes
Peptide units
Peptide bond
Protein synthesis
Ribosomal RNA (rRNA)
RNA catalysis

ARTICLE TITLE: Unusual resistance of peptidyl transferase to protein extraction procedures
AUTHOR: H.F.Noller, V.Hoffarth, and L.Zimniak
JOURNAL: SCIENCE, 256:1416-9 June 5, 1992
ABSTRACT: This paper reports observations about a model system called the peptidyl transferase reaction. This reaction is the source of the catalysis of peptide bonds. It is also the one activity that has been shown to be completely tied to the ribosome structure. This reaction has never been seen outside of the presence of rRNA. The article describes several attempts to remove the peptidyl tranferase activity from a large subunit of the ribosome. Through various attempts and techniques this ability was resistant to removal.
The authors confirm that this activity is probably dependent upon the ribosomal RNA (rRNA). Attempts to study the reactions surrounding peptide bond formation have proven less than successful. No one has been able to duplicate any of the suspected reactions in protein-free preparations of rRNA. It was thought that the rRNA required some of the surrounding proteins found in its natural environment to impliment peptide formation. The 'fragment reaction' requires only the large subunit of the ribosome, appropriate ionic conditions, and some marker substances. It does not need the smaller ribosomal subunit, GTP or even a complete rRNA molecule to progress. After selective protein extractions this reaction was still evident with the large ribosomal subunit. However, the investigators could not be sure that the activity that they saw after extraction was due solely to the rRNA, because there was some polypeptide material present in the milieu. These experiments provide convincing evidence that the rRNA is solely responsible for the formation of peptide bonds.

KEY WORDS/PHRASES
peptide bonds
peptidyl transferase reaction
ribosome
ribosomal RNA (rRNA)

ARTICLE TITLE: How the ribosome moves along the mRNA during protein synthesis
AUTHOR: D. Beyer, E. Skripkin, J. Wadzack, and K.H. Nierhaus
JOURNAL: JOURNAL OF BIOLOGICAL CHEMISTRY, 269(48):30713-7, 12/2/94
ABSTRACT: The movement of the ribosome along the messenger-RNA (mRNA) was assessed by the following experimental strategy. mRNAs were synthesized which contained a short coding sequence with at least four codons. These short strands of mRNA also had unique tags placed on each of their ends. When these mRNAs were allowed to attach themselves to ribosomes in the presence of appropriate transfer-RNAs (tRNAs) the labeled insertion ends of the mRNA were within the ribosomes whereas the long labeled tails extended beyond the ribosomes. These 'tails' were trimmed off and protein synthesis was allowed to progress. After several preparations representing each additional amino acid these tails were trimmed. By analyzing the residues and the remaining lengths of mRNA investigators were able to define the movement of the mRNA through the ribosome. The mRNA enters the ribosome at nucleotide 18 +/- 1 (if the counting starts at the first nucleotide of the P-site codon. The mRNA exits the ribosome at nucleotide -21 +/- 2. The ribosome moves at both sides at once, probably upon the translocation step. This demonstration also shows that most of the mRNA that stretches before and behind the ribosome during protein synthesis is not required for the immediate step. It is postulated that the transfer-RNAs pull the mRNA through the ribosome via codon-anticodon interactions.

KEY WORDS/PHRASES
codons
codon-anticodon interactions
messenger-RNA (mRNA)
nucleotide
ribosome
transfer-RNAs (tRNAs)