↗ RNA distinguishes itself from DNA by its sensitivity towards alkaline caused by an additional OH-group on the ribose.
↗ Detailed chemical analyses revealed that RNA shares three bases with DNA: adenine, cytosine and guanine. In contrast, uracil is unique to RNA whereas thymine is generally present in DNA.
↗ Nucleic acids were isolated from various organisms.
↗ The RNA building blocks ATP and GTP were proposed to be the cell’s general energy source: life’s engine.
↗ Three different species of RNA were identified as translating the genetic information (DNA) into proteins:
• messenger RNA (mRNA) as the carrier of genetic information,
• transfer RNA (tRNA) acting as the physical link between mRNA and protein, and
• ribosomal RNA (rRNA) present in ribosomes, the protein factories.
↗ The genetic code was solved: three bases encode one amino acid.
↗ RNA polymerase, the enzyme synthesizing RNA from a DNA template, was purified.
↗ RNA acts as genetic information in viruses.
↗ Transfer RNA (tRNA) was analyzed:
• tRNAs were sequenced as the first long RNAs.
• The secondary structure of tRNA was predicted by evolutionary comparisons (“tRNA cloverleaf”).
• The tRNA 3d structure was solved by X-ray crystallography (L-shape).
↗ mRNAs were isolated and the addition of non-encoded nucleotides to RNAs (cap, polyA, CCA) was determined.
↗ Reverse transcriptase copying RNA into DNA was characterized.
This weakened the central dogma: DNA makes RNA makes protein.
↗ Introns interrupt genes and have to be removed from RNA transcripts by splicing.
↗ Small RNA-protein complexes are highly abundant in the nucleus and they are essential for pre-mRNA splicing.
↗ The comparison of ribosomal RNA sequences of many organisms provide insight into the evolutionary history of all kingdoms.
↗ RNA by itself is catalytically active: group I, group II introns, RNase P, and hammerhead.
↗ RNA as mobile genetic elements: excised introns can reinsert into the genome.
↗ Spliceosomes are large RNA-protein complexes mediating nuclear pre-mRNA splicing.
↗ Alternative pre-mRNA splicing generates multiple proteins from a single gene.
↗ RNA as a catalytic enzyme and as a genetic element led to the “RNA world hypothesis.”
↗ RNAs can be edited and modified in many different ways within cells.
↗ In vitro selection of RNA molecules (SELEX) allows for the evolution of functional RNA in the test tube.
↗ Chromosome ends are maintained using RNA templates in telomerases.
↗ Ribosomes as the largest RNA enzyme: RNA catalyzes peptide bond formation.
↗ Small RNA molecules regulate gene expression by post-transcriptional gene silencing.
↗ Xist: the first long non-coding RNA regulating gene expression.
↗ Non-coding RNAs control epigenetic phenomena.
↗ Transcriptomics: most of the genome is transcribed at some point in time and space.
↗ Riboswitches bind cellular metabolites and control gene expression.
↗ Many mobile DNA elements use an RNA intermediate.
