ORGANIZATION AND MAINTENANCE OF DROSOPHILA TELOMERES: THE ROLES OF TERMININ AND NON-TERMININ PROTEINS
Grazia D. Raffa, Giovanni Cenci, Laura Ciapponi, Maurizio Gatti
Istituto Pasteur-Fondazione Cenci Bolognetti and Istituto di Biologia e Patologia Molecolari del CNR, Dipartimento di Biologia e Biotecnologie "C. Darwin"; Sapienza, Universita di
Roma, Roma, Italy;
e-mail: maurizio.gatti@uniroma1.it
Drosophila telomeres are elongated by occasional transposition of specialized retroelements rather than telomerase activity, and are assembled independently of the
sequence of the DNA termini. Drosophila telomeres are capped by terminin, a complex formed by the HOAP, Moi, Ver and HipHop proteins that localize exclusively at
telomeres and protect them from fusion events. Other proteins required to prevent end-to-end fusion include HP1, Eff/UbcD1, ATM, the components of the Mre11-Rad50-Nbs (MRN)
complex, and the Woc transcription factor. The terminin proteins are encoded by fast-evolving genes and are not evolutionarily conserved outside the Drosophila species.
In contrast, the non-terminin telomere capping proteins are not fast-evolving, do not localize only at telomeres and are conserved from yeasts to mammals. We propose that following
telomerase loss, Drosophila rapidly evolved terminin to bind chromosome ends in a sequence-independent manner, and that non-terminin proteins did not evolve as rapidly as
terminin because of the functional constraints imposed by their involvement in diverse cellular processes. This hypothesis suggests that the Drosophila non-terminin proteins might
correspond to ancestral telomere-associated proteins with homologues in other organisms including humans.
Key words: terminin, telomeres, telomere fusion, Drosophila
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