PURIFICATION, CHARACTERIZATION AND MOLECULAR-CLONING OF TGP1, A NOVELG-DNA BINDING-PROTEIN FROM TETRAHYMENA-THERMOPHILA

G-DNA, a polymorphic family of four-stranded DNA structures, has been proposed to play roles in a variety of biological processes including telomere function, meiotic recombination and gene regulation. Here we report the purification and cloning of TGP1, a G-DNA specific binding protein from Tetrahymena thermophila, TGP1 was purified by three-colum n chromatographies, including a G-DNA affinity column. Two major prote ins (similar to 80 and similar to 40 kDa) were present in the most hig hly purified column fraction. Renaturation experiments showed that the similar to 80 kDa protein contains TGP1 activity. Biochemical charact erization showed that TGP1 is a G-DNA specific binding protein with a preference for parallel G-DNAs. The TGP1/DNA complex has a dissociatio n constant (K-d) of similar to 2.2 x 10(-8) M and TGP1 can form supers hift in gel mobility shift assays. The cDNA coding TGP1 was cloned and sequenced based upon an internal peptide sequence obtained from the s imilar to 80 kDa protein. Sequence analyses showed that TGP1 is a basi c protein with a pI of 10.58, and contains two extensively hydrophilic and basic domains. Homology searches revealed that TGP1 is a novel pr otein sharing weak similarities with a number of proteins.