Ref ID : 551
Price, C.M. and Cech, T.R.; Telomeric DNA-protein interactions of Oxytricha macronuclear DNA. Genes Dev. 1:783-793, 1987
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Telomeres of Oxytricha macronuclear chromatin exist as discrete nonnucleosomal DNA-protein complexes, each of which encompasses the terminal 100-150 bp of a macronuclear DNA molecule. We have used chemical and nuclease footprinting to examine the internal structure of these telomeric complexes. Remarkably salt-stable DNA-protein interactions result in methylation-protection of specific guanine residues in the 3'-terminal T4G4T4G4 tail. The methylation pattern seen in vivo and in isolated macronuclei is reconstituted in vitro when purified 55-kD and 43-kD telomere proteins are added to purified macronuclear DNA. Very different interactions are observed between protein and DNA within the region approximately 45-135 bp from the 5' terminus. The DNase I cleavage pattern indicates that this DNA lies on the outside surface of protein but is not part of a nucleosome. Our data suggest that the telomeric complexes have two structural domains characterized by their dissimilar DNA-protein interactions. We propose that functionally equivalent telomeres from other organisms could be accommodated in a similar telomeric chromatin structure.