Alternating d(GA·TC)(n) DNA sequences, which are abundant in eukaryotic genomes, can form altered DNA structures. Depending on the environmental conditions, the formation of (GA·GA) hairpins or [C+T(GA·TC)] and [GA(GA·TC)] intramolecular triplexes was observed in vitro. In vivo, the formation of these non-B-DNA structures would likely require the contribution of specific stabilizing factors. Here, we show that Friend's nuclear extracts are rich in proteins which bind the pyrimidine d(TC)(n) strand but not the purine d(GA)(n) strand (NOGA proteins). Upon chromatographic fractionation, four major proteins were detected (NOGA1-4) that have been purified and characterized. Purified NOGAs bind single-stranded d(TC)(n) with high affinity and specificity, showing no significant affinity for either d(GA)(n) or d(GA·TC)(n) DNA sequences. We also show that NOGA1, -2 and -3, which constitute the three most abundant and specific NOGA proteins, correspond to the single-stranded nucleic acid binding proteins hnRNP-L, -K and -I, respectively. These results are discussed in the context of the possible contribution of the NOGA proteins to the stabilization of the (GA·GA) and [GA(GA·TC)] conformers of the d(GA·TC)(n) DNA sequences.
|Journal||Nucleic Acids Research|
|Publication status||Published - 15 Aug 1999|