[Repeating sequences, organizing the telomeric region of chromosomes from the eukaryotic genome]

Abstract

The telomeric regions of the eukaryotic genome are composed of different types of the repeated DNA sequences. Extended subtelomeric repeats (STR) are located close to the terminating repeats (TR) at the extreme ends of the chromosomes. The first part of the review is devoted to the TR sequences. All of them are the simple satellite-similar tandem repeats (T/A)1-8 G1-8. TR, as a substrate of specific telomere elongating enzyme telomerase, controls the whole replication of the chromosomal DNAs. Information accumulated up to this time is sufficient to ascertain the principal uniformity of the structure, the functions and organization of TR in all eukaryotic genomes. The second part of the review is devoted to the STR sequences. The STRs are prolonged repetitive sequences localized between the TR cluster and non-repetitive genes. The STRs have been identified in rye, yeast, Trypanosoma, Drosophila, Chironomus, murine and human genomes. It can be seen from the analysis of experimental results that the STRs of different organisms may have general properties. The information about the functions of STRs is now being obtained for only the STR of Drosophila. The STR is the complex repetitive family located both in telomeres and in heterochromatin. The sequences from the family were recently shown to be capable of translocation and curing destroyed chromosomal ends. According to the latest information, the STR sequences are organized in two different types of clusters in the Drosophila genome. The types have different organization and different genome localization. Is the organization of both telomeric and heterochromatin regions of the Drosophila genome from the same structural elements common for higher eukaryotes or it is the characteristic feature of the Drosophila genome only, is to be cleared.