Abstract
Telomere integrity in Drosophila melanogaster is maintained by a putative multisubunit complex called terminin that is believed to act in analogy to the mammalian shelterin complex in protecting chromosome ends from being recognized as sites of DNA damage. The five proteins supposed to form the terminin complex are HP1-ORC associated protein, HP1-HOAP interacting protein, Verrocchio, Drosophila Telomere Loss/Modigliani and Heterochromatic Protein 1. Four of these proteins evolve rapidly within the Drosophila genus. The accelerated evolution of terminin components may indicate the involvement of these proteins in the process by which new species arise, as the resulting divergence of terminin proteins might prevent hybrid formation, thus driving speciation. However, terminin is not an experimentally proven entity, and no biochemical studies have been performed to investigate its assembly and action in detail. Motivated by these facts in order to initiate biochemical studies on terminin function, we attempted to reconstitute terminin by co-expressing its subunits in bacteria and investigated the possible role of the fast-evolving parts of terminin components in complex assembly. Our results suggest formation of stable subcomplexes of terminin, but not of the whole complex in vitro. We found that the accelerated evolution is restricted to definable regions of terminin components, and that the divergence of D. melanogaster Drosophila Telomere Loss and D. yakuba Verrocchio proteins does not preclude their stable interaction.
Highlights
The ends of the linear genetic material represent two problems regarding their faithful maintenance throughout cell generations
Though our system is limited in this respect, existing data on pairwise interactions between terminin proteins suggest that the presence of HipHop might not be an absolute requirement for complex formation, and a heterotetramer terminin subcomplex may form in the absence of HipHop
We did not observe the presence of a tetrameric complex during purification of four co-expressed capping proteins, but detected subcomplexes consisting of Ver-Drosophila Telomere Loss (DTL)/Moi and Heterochromatic Protein 1 (HP1)-ORC associated protein (HOAP)-HP1
Summary
The ends of the linear genetic material represent two problems regarding their faithful maintenance throughout cell generations. Drosophila Telomere Protein Complex Assembly normal cell cycle [3]. These problems have been circumvented during eukaryotic evolution by the “invention” of the telomere and its associated proteins. It has been proposed that the single-stranded part of the telomere (3’-overhang) folds back to its homologous sequence and hybridizes to its complement while displacing the identical strand. This DNA structure is called a t-loop [5]; it prevents the end from being recognized by components of DNA repair and checkpoint processes as a double-stranded DNA break [6, 7]
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