Functional diversification of yeast telomere associated protein, Rif1, in higher eukaryotes.
BACKGROUND
Telomeres are nucleoprotein complexes at the end of linear eukaryotic chromosomes which maintain the genome integrity by regulating telomere length, preventing recombination and end to end fusion events. Multiple proteins associate with telomeres and function in concert to carry out these functions. Rap1 interacting factor 1 (Rif1), was identified as a protein involved in telomere length regulation in yeast. Rif1 is conserved upto mammals but its function has diversified from telomere length regulation to maintenance of genome integrity.


RESULTS
We have carried out detailed bioinformatic analyses and identified Rif1 homologues in 92 organisms from yeast to human. We identified Rif1 homologues in Drosophila melanogaster, even though fly telomeres are maintained by a telomerase independent pathway. Our analysis shows that Drosophila Rif1 (dRif1) sequence is phylogenetically closer to the one of vertebrates than yeast and has identified a few Rif1 specific motifs conserved through evolution. This includes a Rif1 family specific conserved region within the HEAT repeat domain and a motif involved in protein phosphatase1 docking. We show that dRif1 is nuclear localized with a prominent heterochromatin association and unlike human Rif1, it does not respond to DNA damage by localizing to damaged sites. To test the evolutionary conservation of dRif1 function, we expressed the dRif1 protein in yeast and HeLa cells. In yeast, dRif1 did not perturb yeast Rif1 (yRif1) functions; and in HeLa cells it did not colocalize with DNA damage foci.


CONCLUSIONS
Telomeres are maintained by retrotransposons in all Drosophila species and consequently, telomerase and many of the telomere associated protein homologues are absent, including Rap1, which is the binding partner of Rif1. We found that a homologue of yRif1 protein is present in fly and dRif1 has evolutionarily conserved motifs. Functional studies show that dRif1 responds differently to DNA damage, implying that dRif1 may have a different function and this may be conserved in other organisms as well.
Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad, 500046, India.
Easwaran
E
Sreesankar
Ramamoorthy
R
Senthilkumar
Vellaichamy
V
Bharathi
Rakesh K
RK
Mishra
Krishnaveni
K
Mishra
D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019295:Computational Biology; D004249:DNA Damage; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D019143:Evolution, Molecular; D006367:HeLa Cells; D006801:Humans; D010802:Phylogeny; D011485:Protein Binding; D054645:Protein Phosphatase 1 / Q000737:chemistry / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D018626:Retroelements; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism
D002352:Carrier Proteins; D029721:Drosophila Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D018626:Retroelements; C000606084:Rif1 protein, Drosophila; D029701:Saccharomyces cerevisiae Proteins; D034501:Telomere-Binding Proteins; C074461:RIF1 protein, S cerevisiae; D054645:Protein Phosphatase 1