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A mobile dispersed genetic element, mdg4 , approximately 7.5 kilobases (kb) long has been cloned from D. melanogaster genome. Chromosomal bands have only few sites of mdg4 , but it always hybridizes to the chromocenter. The location of mdg4 varies among D. melanogaster strains. Blot hybridization shows that, in contrast to other mdg elements, mdg4 sequences are rather heterogeneous. Only few copies are full-length. A strong amplification of mdg4 has occurred during the in vitro cultivation of cells involving only one mdg4 variant. Long terminal repeats (LTRs) and flanking sequences have been sequenced in two cloned copies of transposable element mdg4 . In both cloned copies of mdg4 , LTRs have an identical nucleotide sequence 479 bp long. The mdg4 is flanked by four-base-pair direct repeats, short mismatched palindromes being present at the ends of each LTR. The termini of the mdg4 body contain an oligopurine stretch and a region partially complementary to D. melanogaster tRNA-Lys. Thus, structural organization of mdg4 LTRs is similar to that of several other mdg elements and retroviral proviruses.

1. The addition of tRNA to chromatin gel (initial insoluble deoxyribonucleoprotein preparation) in the presence of 1 mM MgC1, or of 40 mM NaCl results in the transfer of the very lysinerich histone (Fl) and of some nonhistone proteins to the tRNA, whereas all other histones remain in the deoxyribonucleoprotein. This result provides a new general method for the mild removal of histone F1 from the chromatin gel. The addition of tRNA to chromatin gel in the absence of Mga+ and Na+ results not only in the rapid removal of histone F1 and of some nonhistone proteins from the chromatin gel, but also in the slow transfer of histones F2a2 and F2b to the tRNA. A similar pattern of histone redistribution is observed when the tRNA (or DNA) is added to the soluble deoxyribonucleoprotein preparation obtained by mechanical disruption of the chromatin gel.2. There is no protein redistribution in the above-mentioned soluble deoxyribonucleoprotein preparation (in the absence of exogeneous free polynucleotides).3. The addition of free DNA or tRNA to the soluble deoxyribonucleoprotein preparation, obtained by treatment of the chromatin gel with 2 M urea, allows one to remove quantitatively histones F1, F2a2 and F2b from the deoxyribonucleoprotein, leaving the initial distribution of the arginine-rich histones (F2al and F3) on the endogeneous DNA unchanged.4. The redistribution of proteins (and in particular of histones) occurs in the soluble deoxyribonucleoprotein preparation obtained by urea treatment even in the absence of any exogeneous polynucleotides suggesting that conservation of the initial distribution of proteins in this soluble deoxyribonucleoprotein preparation is not complete. 16.close to the initial native deoxyribonucleoprotein, i.e. that no redistribution of proteins occurs during or after the isolation procedure.Jensen and Chalkley [12] have shown that the introduction of free DNA into the soluble deoxyribonucleoprotein preparation (obtained by mechanical disruption ofthe chromatin gel) results in the transfer ofa part of the lysine-rich histone to exogeneous DNA. However, no further analysis of this phenomenon was carried out. I n the present paper the question is studied in more detail in order to characterize the features of the interactions between deoxyribonucleoprotein and free DNA or RNA and also between Merent deoxyribonucleoprotein molecules in the soluble preparations.The following questions were analysed. (a) What is the pattern of protein redistribution in the soluble deoxyribonucleoprotein preparations containing exogeneous free DNA or RNA? (b) Does the possibility of the transfer of proteins from the chromatin gel (initial insoluble deoxyribonucleoprotein preparation) to the free DNA or RNA exist ? (c) Does any redistribution of proteins in the soluble deoxyribonucleoprotein preparations occur?

The gypsy (mdg4) mobile element of Drosophila contains two closely spaced regions which bind proteins from nuclear extracts. One of these is an imperfect palindrome having homology with the lac‐operator of Escherichia coli; the other contains a reiterated sequence (5′PyPuT/C TGCATAC/TPyPy) homologous to the octamer that is the core of many enhancers and upstream promoter elements. Transient expression of deletion mutants has shown that these DNA regions are negative and positive regulators of transcription. As was demonstrated earlier by other authors, mutations induced by the presence of gypsy in different loci are suppressed owing to either repression or activation of gypsy transcription in Drosophila strains carrying unlinked mutations in su(Hw) or su(f) genes. We have shown that binding to a negative regulator (silencer) is weakened in nuclear extracts isolated from fly stocks carrying su(f) mutations which activate gypsy transcription; therefore the su(f) gene seems to code for a protein capable of gypsy repression. Furthermore, binding to a positive regulator is weakened in nuclear extracts isolated from fly stocks carrying su(Hw) gene mutations which decrease the level of gypsy transcription; therefore, the su(Hw) gene most likely encodes a protein which activates gypsy transcription.

The paper discusses the techniques which are currently implemented for vaccine production based on virus-like particles (VLPs). The factors which determine the characteristics of VLP monomers assembly are provided in detail. Analysis of the literature demonstrates that the development of the techniques of VLP production and immobilization of target antigens on their surface have led to the development of universal platforms which make it possible for virtually any known antigen to be exposed on the particle surface in a highly concentrated form. As a result, the focus of attention has shifted from the approaches to VLP production to the development of a precise interface between the organism's immune system and the peptides inducing a strong immune response to pathogens or the organism's own pathological cells. Immunome-specified methods for vaccine design and the prospects of immunoprophylaxis are discussed. Certain examples of vaccines against viral diseases and cancers are considered.

The structural organization of the retrotransposon gypsy (mdg4) is investigated in two Drosophila melanogaster strains. One of them, the stable w strain (SS), is characterized by a small copy number and stable localization of gypsy. In the other, unstable mutator strain (MS) which is derived from SS, the gypsy copy number and the frequency of its transposition are greatly increased. Genomic gypsy copies cloned from both strains display structural differences allowing them to be divided into two subfamilies. At the nucleotide level, these differences involve single substitutions, deletions and insertions. Southern blot analysis revealed that SS possesses only gypsy elements that belong to one subfamily, while in MS only gypsy copies from the other subfamily were amplified and transposed. The transcriptional activity of gypsy was also studied. Despite the structural differences, plasmid-borne copies of each type of gypsy exhibit equal transcriptional activity in transfected tissue culture cells. Nevertheless, although a high level of gypsy transcription is observed in MS, gypsy poly(A)+RNA is not detected in SS.