A combinatorial method to isolate short ribozymes from complex ribozyme libraries

Weak effects of prebiotically plausible peptides on self-triphosphorylation ribozyme function

Catalytic RNAs (ribozymes) were central to early stages of life on earth. The first ribozymes probably emerged in the presence of prebiotically generated peptides because amino acids can be generated under abiotic conditions, and amino acids can oligomerize into peptides under prebiotically plausible conditions. Here we tested whether the presence of prebiotically plausible peptides could have aided the emergence of ribozymes, by an in vitro selection of self-triphosphorylation ribozymes from random sequence in the presence of ten different octapeptides. These peptides were composed of ten different, prebiotically plausible amino acids, each as mixture of d- and l-stereoisomers. After five rounds of selection and high throughput sequencing analysis, ten ribozymes that appeared most promising for peptide benefits were tested biochemically for possible benefits from each of the ten peptides. The strongest peptide benefit enhanced ribozyme activity by 2.6-fold, similar to the effect from an increase in the pH by one-half unit. Four arbitrarily chosen ribozymes from a previous selection without peptides showed no significant change in their activity in the presence of the ten peptides. Therefore, the used prebiotically plausible peptides - peptides without evolutionarily optimized sequence, without cationic or aromatic side chains - did not provide a strong benefit for the emergence of ribozyme activity. This finding stands in contrast to previously identified polycationic peptides, conjugates between peptides and polyaromatic hydrocarbons, and modern mRNA encoded proteins, all of which can strongly increase ribozyme function. The results are discussed in the context of origins of life.

Peptide conjugates with polyaromatic hydrocarbons can benefit the activity of catalytic RNAs

Early stages of life likely employed catalytic RNAs (ribozymes) in many functions that are today filled by proteins. However, the earliest life forms must have emerged from heterogenous chemical mixtures, which included amino acids, short peptides, and many other compounds. Here we explored whether the presence of short peptides can help the emergence of catalytic RNAs. To do this, we conducted an in vitro selection for catalytic RNAs from randomized sequence in the presence of ten different peptides with a prebiotically plausible length of eight amino acids. This in vitro selection generated dozens of ribozymes, one of them with ∼900-fold higher activity in the presence of one specific peptide. Unexpectedly, the beneficial peptide had retained its N-terminal Fmoc protection group, and this group was required to benefit ribozyme activity. The same, or higher benefit resulted from peptide conjugates with prebiotically plausible polyaromatic hydrocarbons (PAHs) such as fluorene and naphthalene. This shows that PAH-peptide conjugates can act as potent cofactors to enhance ribozyme activity. The results are discussed in the context of the origin of life.

Construction and Application of Orthogonal T7 Expression System in Eukaryote: An Overview

The T7 system is an orthogonal transcription-system, which is characterized by simplicity, higher efficiency, and higher processivity, and it is used for protein or mRNA synthesis in various biological-systems. In comparison with prokaryotes, the construction of the T7 expression system is still on-going in eukaryotes, but it shows greatly applicable prospects. In the present paper, development of T7 expression system construction in eukaryotes is reviewed, including its construction in animal (mammalian cells, trypanosomatid protozoa, Xenopus oocytes, zebrafish), plant, and microorganism and its application in vaccine production and gene therapy. In addition, the innate challenges of T7 expression system construction in eukaryote and its potential application in vaccine production and gene therapy are discussed.

Secondary Structure Libraries for Artificial Evolution Experiments

Methods of artificial evolution such as SELEX and in vitro selection have made it possible to isolate RNA and DNA motifs with a wide range of functions from large random sequence libraries. Once the primary sequence of a functional motif is known, the sequence space around it can be comprehensively explored using a combination of random mutagenesis and selection. However, methods to explore the sequence space of a secondary structure are not as well characterized. Here we address this question by describing a method to construct libraries in a single synthesis which are enriched for sequences with the potential to form a specific secondary structure, such as that of an aptamer, ribozyme, or deoxyribozyme. Although interactions such as base pairs cannot be encoded in a library using conventional DNA synthesizers, it is possible to modulate the probability that two positions will have the potential to pair by biasing the nucleotide composition at these positions. Here we show how to maximize this probability for each of the possible ways to encode a pair (in this study defined as A-U or U-A or C-G or G-C or G.U or U.G). We then use these optimized coding schemes to calculate the number of different variants of model stems and secondary structures expected to occur in a library for a series of structures in which the number of pairs and the extent of conservation of unpaired positions is systematically varied. Our calculations reveal a tradeoff between maximizing the probability of forming a pair and maximizing the number of possible variants of a desired secondary structure that can occur in the library. They also indicate that the optimal coding strategy for a library depends on the complexity of the motif being characterized. Because this approach provides a simple way to generate libraries enriched for sequences with the potential to form a specific secondary structure, we anticipate that it should be useful for the optimization and structural characterization of functional nucleic acid motifs.