Amplification of regions of the genome in the somatic cells of mammals resistant to colchicine. VII. Localization of the initial and amplified copies of gene mdr in one and the same segment of chromosome 4 of the Djungarian hamster

By in situ hybridization technique, the mdr gene which is amplified during the development of multiple drug resistance was mapped in the 4q15--21 segment of normal Djungarian hamster chromosome 4. As was shown earlier, this chromosomal region is specific for the location of amplified mdr gene copies. These results, as well as some data obtained by other authors, suggest that recombinations of amplified DNAs occur preferentially in or near the sites bearing homologous sequences.     

Status of collective immunity to hepatitis A virus in urban residents in Byelorussia]

The large immune stratum and intense collective immunity to virus hepatitis A among the urban population of Byelorussia are characteristic of hyperendemic territory. The geometric mean of the antibody titer has been noted to increase with age, which is probably due to repeated infections of persons who have already had the disease. The use of this value for the characterization of collective immunity and epidemiological situation has been proposed.     

The L7/L12 proteins change their conformation upon interaction of EF-G with ribosomes

The different functional complexes of ribosomes with elongation factor F (EF-G) were studied by digestion experiments with trypsin. It was found that upon interaction of EF-G with ribosomes the L7/L12 proteins are sensitive to trypsin and are trypsin resistant after dissociation of EF-G from ribosomes. The significance of conformational alterations in the L7/L12 and also in the other proteins in the translation process is discussed.     

Novel data on interactions of elongation factor Ts.

Interactions of EF-Ts with EF-Tu at all steps of the elongation cycle were studied by limited trypsinolysis, gel-filtration, analytical centrifugation and fluorescence polarization techniques. It is shown that EF-Ts does not dissociate from EF-Tu after GDP to GTP exchange, but remains bound to the Aa-tRNA.EF-Tu.GTP complex up to GTP hydrolysis stage on the ribosome. The possible role of these interactions is discussed.     

Characteristics of inheritance of restriction fragment polymorphisms for non-transcribed spacers of human rRNA genes

Inheritance of polymorphous restricts of nontranscribed spacer (NTS) located to the right from 3'-end of 28S rRNA gene has been studied in families. Single classes of NTS polymorphous fragments are presented in the genome by some tenths of copies and are inherited as a simple mendelian characteristic located on separate chromosomes.     

Dimer state of protein L7/L12 and EF-G-dependent reactions of ribosomes.

A number of different monomer and dimer derivatives of protein L7/L12 has been studied in EF-G-dependent reactions on the ribosome. It has been shown that only dimer derivatives of protein L7/L12 are able to interact with the ribosome. This means that it is the dimer forms of protein L7/L12 that are present in the functionally active ribosome. It is likely that the N-terminal sequence of protein L7/L12 is responsible for dimerization of the protein in solution and at the same time contributes mainly to the interaction of the protein L7/L12 dimer with the ribosome. The results obtained suggest that there are four copies of protein L7/L12 in the translating ribosome.     

Domain IV of elongation factor G from Thermus thermophilus is strictly required for translocation.

Two truncated variants of elongation factor G from Thermus thermophilus with deletion of its domain IV have been constructed and the mutated genes were expressed in Escherichia coli. The truncated factors were produced in a soluble form and retained a high thermostability. It was demonstrated that mutated factors possessed (1) a reduced affinity to the ribosomes with an uncleavable GTP analog and (2) a specific ribosome-dependent GTPase activity. At the same time, in contrast to the wild-type elongation factor G, they were incapable to promote translocation. The conclusions are drawn that (1) domain IV is not involved in the GTPase activity of elongation factor G, (2) it contributes to the binding of elongation factor G with the ribosome and (3) is strictly required for translocation. These results suggest that domain IV might be directly involved in translocation and GTPase activity of the factor is not directly coupled with translocation.