STRUCTURE OF A PARALLEL-STRANDED TETRAMER OF THE OXYTRICHA TELOMERIC DNA-SEQUENCE DT4G4

We report here the determination of the solution structure of the sing le-copy tetramer of the sequence dT4G4, the unit repeat in telomeres o f the ciliated protozoan Oxytricha, in the presence of potassium ions. This is accomplished by a combination of sequential assignments and d istance determinations from 2D proton NMR with model building, based o n conformational analysis of the structure using a full-matrix NOESY s imulation and molecular dynamics. Each strand in this tetramer structu re has an identical environment and conformation: a parallel-stranded, right-handed helix, with all nucleotides in the C2'-endo, anti config uration. The T flanking the G cluster stacks in a 4-fold symmetrical h elical array, while the remaining T's become increasingly flexible and sample multiple stacked configurations.