The gene of the hybrid protein that encodes the double synthetic fragment proZZ of the immunoglobulin-binding domain of protein A of Staphylococcus aureus and apo-obelin joined by a short linker has been cloned. The corresponding hybrid protein has been obtained by expression in Esсheriсhia coli cells. The protein activated with a substrate (coelenterazine) possesses the bioluminescent Са2+-dependent activity of the photoprotein close to that of recombinant wild-type obelin, and the immunoglobulin-binding ability of protein A. It has been shown that the hybrid can be used as a highly sensitive label to detect antibodies and estimate their affinity and interaction with recombinant proteins, as well as in investigations of other kinds.

The ability of a series of novel modified external guide sequences (EGS oligonucleotides) to induce the hydrolysis of target RNA with bacterial ribonuclease P has been studied; the most efficient modification variants have been selected. We have found patterns of the oligonucleotide sugar-phosphate backbone modi-fications that enhance oligonucleotide stability in the biological environment and do not violate the ability to interact with the enzyme and induce the RNA hydrolysis. It has been shown that analogues of EGS oligonucleotides selectively modified at 2'-position (2'-O-methyl and 2'-fluoro) or at internucleotide phosphates (phosphoryl guanidines) can be used for the addressed cleavage of a model RNA target by bacterial RNase P. The ability of new phosphoryl guanidine analogues of oligodeoxyribonucleotides that are stable in biological media to induce the hydrolysis of target RNA with bacterial ribonuclease P has been shown for the first time. The modified EGS oligonucleotides with an optimal balance between functional activity and stability in biological media can be considered as potential antibacterial agents.

A variant of the Ca2+-regulated photoprotein obelin elongated with a hexahistidine peptide from the N-terminus was developed and studied. After immobilization on a metal-affine sorbent, the hybrid protein was applied as a target for the in vitro selection of RNA aptamers. According to the data of bioluminescent solid-phase microanalysis, the selection was shown to enrich the RNA library with obelin-affine molecules.

The properties of hammerhead ribozymes are described. Various hammerhead ribozyme constructs for target RNA cleavage were considered. Approaches to enhancement of the stability of artificial ribozymes in biological media and to regulation of the catalytic activity of hammerhead ribozymes using effector molecules are described. The effect of ribozymes on extended structured natural RNAs is discussed. Applications of artificial hammerhead ribozymes as inhibitors of gene expression at matrix RNA level were considered.

Escort aptamers are DNA or RNA sequences with high affinity to certain cell-surface proteins, which can be used for targeted delivery of various agents into cells of a definite type. The peculiarities of the selection of escort aptamers are discussed in this review. The methods used in selection of escort aptamers via the SELEX technique are considered, including selection against isolated cell-surface proteins, cell fragments, living eukaryotic cells, and bacteria. Particular attention is given to the design and chemical modification of escort aptamers. The different fields of application of escort aptamers are described, including the targeted delivery of siRNAs, nanoparticles, toxins, and photoagents, as well as the identification of specific cell markers and the detection or isolation of cells of a definite type. The potential for the application of escort aptamers in the development of new therapeutic agents and diagnostic systems is also discussed.

Trans hammerhead ribozymes are considered from the point of view of the RNA world theory. An attempt was made to reconstruct the ‘ancestors’ of contemporary hammerhead ribozymes with improved ligation activity by altering the sequence of trans hammerhead motifs. RNA ligation activity of trans hammerheads was shown to be affected significantly by minor changes in non-conservative regions. In particular, introduction of heptanucleotide bulge into stem III led to the 10-fold increase of ligation rate constant. At that, RNA cleavage was predominant activity in all cases. It was shown that trans hammerhead ribozyme can assemble from two separate short oligoribonucleotides upon binding to RNA substrate. This binary hammerhead ribozyme possesses a higher RNA-cleaving activity than its full-length analog. It can be assumed that such self-assembling multi-subunit catalytic RNAs could exist at early stages of the prebiotic evolution.