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Abstract

Microsatellites or simple sequence repeats (SSRs) are ubiquitous in genomes studied so far. SSR mutations or microsatellite instability (MSI) can result in either expansion or contraction of repeat units. These alterations can lead to disorders like cancer and neurodegeneration. As gleaned from studies, it appears that SSR mutations are dependent on motif size, nucleotide content and SSR length. Besides these, position of SSRs in genome (coding or non-coding sequences), presence on leading or lagging strand and distance from origin of replication also affect SSR mutations. Further, fidelity of replication and repair machinery as well as epigenetic factors may influence repeat stability. This review summarizes some of these aspects of SSR mutations that occur especially during DNA replication/repair besides epigenetic factors that influence SSR contraction or expansion.

Keywords: Simple sequence repeats, microsatellites, DNA polymerase, DNA repair, strand slippage

Mikrosatelit veya Basit Dizi Tekrar (SSR) karars?zl?klar? replikasyon ve tamir s?ras?nda tekrar karakteristiklerine bagl?d?r

Özet

Mikrosatelit veya Basit Dizi Tekrarlar? (SSR) simdiye kadar çal?s?lan genomlar?n hepsinde bulunur. SSR mutasyonlar? veya mikrosatelit karars?zl?g? (MSI) tekrar ünitelerinin uzamas?na yada k?salmas?na sebep olur. Bu alterasyonlar kanser ve nörodejenerasyon gibi rahars?zl?klara yol açarlar. Çal?smalardan anlas?ld?g? gibi, SSR mutasyonlar?, motif büyüklügüne, nükleotid içerigine ve SSR uzunluguna bagl? görünmektedir. Bunlar?n yan?nda, genomda SSR pozisyonlar? (kodlanan veya kodlanmayan), kesintizin ya da kesintili zincirde varl?g? ve replikasyon orijine uzakl?g? da SSR mutasyonlar?n? etkiler. Bununla beraber, replikasyonun ve tamir makinas?n?n dogrulugu epigenetik faktörler gibi tekrar kararl?l?g?n? etkiler. Bu derleme makale, epigenetik faktörlerden ziyade özellikle DNA replikasyonu/ tamiri s?ras?nda olusan SSR mutasyonlar?n?n SSR uzama ve k?salmas?n? etkileyen yönlerinden baz?lar?n? özetler.

Anahtar Sözcükler: Basit dizi tekrarlar?, mikrosatelitler, DNA polimeraz, DNA tamiri, zincir kaymas?

Introduction

Microsatellites or Simple Sequence Repeats

SSRs or microsatellites are tandem repeats of 2-8nt units of DNA and are ubiquitous in all genomes studied so far. SSR have varying density and motif distribution that may be species specific even in genomes with low SSR density. For example, among Eukaryotes, bivalves have one of the lowest SSR densities but molluscan specific repeat density variations are reported (Cruz et al., 2005). Similarly, variations are seen in SSRs in mitochondrial DNA of Procypris rabaudi (Tchang) (an endemic fish species in China), (Zhang et al., 2009). These species specific variations can be explained on the basis of differences...

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