Recurring features of local tertiary structural elements in RNA molecules exemplified by hepatitis D virus RNA.

Elements of local tertiary structure in RNA molecules are important in understanding structure-function relationships. The loop E motif, first identified in several eukaryotic RNAs at functional sites which share an exceptional propensity for UV crosslinking between specific bases, was subsequently shown to have a characteristic tertiary structure. Common sequences and secondary structures have allowed other examples of the E-loop motif to be recognized in a number of RNAs at sites of protein binding or other biological function. We would like to know if more elements of local tertiary structure, in addition to the E-loop, can be identified by such common features. The highly structured circular RNA genome of the hepatitis D virus (HDV) provides an ideal test molecule because it has extensive internal structure, a UV-crosslinkable tertiary element, and specific sites for functional interactions with proteins including host PKR. We have now found a UV-crosslinkable element of local tertiary structure in antigenomic HDV RNA which, although differing from the E-loop, has a very similar pattern of sequence and secondary structure to the UV-crosslinkable element found in the genomic strand. Despite the fact that the two structures map close to one another, the sequences comprising them are not the templates for each other. Instead, the template regions for each element are additional sites for potential higher order structure on their respective complementary strands. This wealth of recurring sequences interspersed with base-paired stems provides a context to examine other RNA species for such features and their correlations with biological function.

Ribonucleoprotein complexes of hepatitis delta virus.

Human hepatitis delta virus (HDV) is a subviral satellite agent of hepatitis B virus (HBV). The envelope proteins of HDV are provided by the helper virus, HBV, but very little is known about the internal structure of HDV. The particles contain multiple copies of the delta antigen and an unusual RNA genome that is small, about 1,700 nucleotides in length, single stranded, and circular. By using UV cross-linking, equilibrium density centrifugation, and immunoprecipitation, we obtained evidence consistent with the interpretation that delta antigen and genomic RNA form a stable ribonucleoprotein (RNP) complex within the virion. Furthermore, electron-microscopic examination of the purified viral RNP revealed a roughly spherical core-like structure with a diameter of 18.7 +/- 2.5 nm. We also isolated HDV-specific RNP structures from the nuclei of cells undergoing HDV genome replication; both the genome and antigenome (a complement of the genome) of HDV were found to be in such complexes. From the equilibrium density analyses of the viral and nuclear RNPs, we were able to deduce the number of molecules of delta antigen per molecule of HDV RNA. For virions, this number was predominantly ca. 70, which was larger than for the nuclear RNPs, which were more heterogeneous, with an average value of ca. 30.

[Effect of gamma radiation on the components of hepatitis B virus and the delta antigen]. / Vliianie gamma-izlucheniia na komponenty virusa gepatitia B i del'ta-antigen.

The influence of ionizing irradiation on the serological activity of purified HBsAg, receptors to polymerized albumin, DNA-polymerase activity, delta agent, and delta antigen was studied. Different radiosensitivity of hepatitis B virus components and delta-system was demonstrated. The possibility of sterilization by irradiation of purified HBsAg preparations suitable for construction of a vaccine against hepatitis B was shown.