At the Beginning of the End and in the Middle of the Beginning: Structure and Maintenance of Telomeric DNA Repeats and Interstitial Telomeric Sequences

Abstract

Tandem DNA repeats derived from the ancestral (TTAGGG)n run were first detected at chromosome ends of the majority of living organisms, hence the name telomeric DNA repeats. Subsequently, it has become clear that telomeric motifs are also present within chromosomes, and they were suitably called interstitial telomeric sequences (ITSs). It is well known that telomeric DNA repeats play a key role in chromosome stability, preventing end-to-end fusions and precluding the recurrent DNA loss during replication. Recent data suggest that ITSs are also important genomic elements as they confer its karyotype plasticity. In fact, ITSs appeared to be among the most unstable microsatellite sequences as they are highly length polymorphic and can trigger chromosomal fragility and gross chromosomal rearrangements. Importantly, mechanisms responsible for their instability appear to be similar to the mechanisms that maintain the length of genuine telomeres. This review compares the mechanisms of maintenance and dynamic properties of telomeric repeats and ITSs and discusses the implications of these dynamics on genome stability.

Telomeres and Telomere Length: A General Overview

“…The telomeres in yeast comprise of GGTTACA repeat sequences that extend up to 300 bp [7,8]. In plants, TTTAGGG repeats typically range between 2 to 100 kb, and certain protozoan and fungi carry short telomeres ranging between 18 to 600 bp [9,10]. In vertebrates, chromosomal ends consist of TTAGGG repeats with the longest telomeres being in rats and some strains of Mus musculus that extend up to 150 kb [5,7].…”

Insight into the Chromosome Structure of the Cultivated Tetraploid Alfalfa (Medicago sativa subsp. sativa L.) by a Combined Use of GISH and FISH Techniques

“…The localization of telomeric repeats in proximity of the nucleolar constrictions, as in alfalfa, has also been found in other organisms. That telomeric sequences and specifically ITSs might play a role in nucleolus organization is an accepted possibility [27]. The results of this study indicate that M. sativa subsp.…”

Structures and stability of simple DNA repeats from bacteria

“…For example, simple repeats that are rich in G bases on one strand (and C bases on the other) are often located at the ends of chromosomes. Known as telomeres, these repeats have been best characterized in the genomes of eukaryotes [22], but they also occur in some bacteria [12,13].…”

“…For example, simple repeats that are rich in G bases are often found at telomeric ends of chromosomes and there is significant evidence that such sequences form complexes of proteins specifically bound to four-stranded structures [46]. Telomeres have been best characterized in the genomes of eukaryotes, including humans, but they also occur in some bacteria [12,13,22].…”