A tribute to Sidney Altman, one of the architects of modern RNA biology.

This special issue of JBC pays tribute to Sidney Altman, whose discovery of a catalytic role for RNA, a breakthrough made independently by Thomas Cech, overturned the long-held dogma that only proteins can serve as catalysts in biological systems. The discovery of RNA catalysis galvanized biologists to think expansively in new directions and has given rise to a remarkable RNAissance in science and medicine. The collection of articles begins with the story of the discovery of RNase P and builds up to the emerging picture of an unexpectedly vast repertoire of RNase P variants in the three domains of life, including insights derived from recent high-resolution structures on how RNAs, ribonucleoproteins, or protein scaffolds can be used variably to generate an active site for catalyzing the same RNA processing reaction. The series of articles ends with a discussion of more recently discovered endonucleases (Argonautes, Cas), whose parallels with RNase P underscore recurring themes in diverse biological contexts.

How to Kinetically Dissect an RNA Machine.

RNA-based machines are ubiquitous in Nature and increasingly important for medicines. They fold into complex, dynamic structures that process information and catalyze reactions, including reactions that generate new RNAs and proteins across biology. What are the experimental strategies and steps that are necessary to understand how these complex machines work? Two 1990 papers from Herschlag and Cech on "Catalysis of RNA Cleavage by the Tetrahymena thermophila Ribozyme" provide a master class in dissecting an RNA machine through kinetics approaches. By showing how to propose a kinetic framework, fill in the numbers, do cross-checks, and make comparisons across mutants and different RNA systems, the papers illustrate how to take a mechanistic approach and distill the results into general insights that are difficult to attain through other means.

The Hammerhead Ribozyme: A Long History for a Short RNA.

Small nucleolytic ribozymes are a family of naturally occurring RNA motifs that catalyse a self-transesterification reaction in a highly sequence-specific manner. The hammerhead ribozyme was the first reported and the most extensively studied member of this family. However, and despite intense biochemical and structural research for three decades since its discovery, the history of this model ribozyme seems to be far from finished. The hammerhead ribozyme has been regarded as a biological oddity typical of small circular RNA pathogens of plants. More recently, numerous and new variations of this ribozyme have been found to inhabit the genomes of organisms from all life kingdoms, although their precise biological functions are not yet well understood.

The Cech Symposium: a celebration of 25 years of ribozymes, 10 years of TERT, and 60 years of Tom.

The Cech Symposium was held in Boulder, Colorado, on July 12-13, 2007, to celebrate a triple anniversary: 25 years since the first publication reporting RNA self-splicing, 10 years since the identification of reverse transcriptase motifs in the catalytic subunit of telomerase, and 60 years since the birth of Thomas R. Cech. Past and present members of the Cech laboratory presented on their current research, which branched into many categories of study including RNA-mediated catalysis, telomerase and telomeres, new frontiers in nucleic acids, alternative splicing, as well as scientific research with direct medical applications.

How the discovery of ribozymes cast RNA in the roles of both chicken and egg in origin-of-life theories.

Scientific theories about the origin-of-life theories have historically been characterized by the chicken-and-egg problem of which essential aspect of life was the first to appear, replication or self-sustenance. By the 1950s the question was cast in molecular terms and DNA and proteins had come to represent the carriers of the two functions. Meanwhile, RNA, the other nucleic acid, had played a capricious role in origin theories. Because it contained building blocks very similar to DNA, biologists recognized early that RNA could store information in its linear sequences. With the discovery in the 1980s that RNA molecules were capable of biological catalysis, a function hitherto ascribed to proteins alone, RNA took on the role of the single entity that could act as both chicken and egg. Within a few years of the discovery of these catalytic RNAs (ribozymes) scientists had formulated an RNA World hypothesis that posited an early phase in the evolution of life where all key functions were performed by RNA molecules. This paper traces the history the role of RNA in origin-of-life theories with a focus on how the discovery of ribozymes influenced the discourse.

The biochemical roots of the RNA world: from zymonucleic acid to ribozymes.

The history of the ideas that led to the RNA World hypothesis is reviewed. As the understanding of the properties of RNA molecules progressed, the evolutionary interpretation of their genetic properties and widespread distribution in intracellular environments, as well as the catalytic properties of nucleotide coenzymes and the participation of RNA monomers in metabolic pathways, led to several independent proposals of protein-free primordial life forms. Current ideas on the RNA World are part of a long and storied scientific perspective in which these different hypotheses were developed. However, the lack of continuity between them may be explained in part by the absence of an evolutionary framework that characterized the early development of molecular biology, as well as by the demise of certain areas of research like coenzyme chemistry.