IDENTIFICATION AND CHARACTERIZATION OF A CELL-MEMBRANE NUCLEIC-ACID CHANNEL

We have identified a 45-kDa protein purified from rat renal brush bord er membrane that binds short single-stranded nucleic acid sequences. T his activity was purified, reconstituted in proteoliposomes, and then fused with model planar lipid bilayers, In voltage-clamp experiments, the reconstituted 45-kDa protein functioned as a gated channel that al lows the passage of nucleic acids, Channel activity was observed immed iately after addition of oligonucleotide. Channel activity was not obs erved in the absence of purified protein or of oligonucleotide or when protein was heat-inactivated prior to forming proteoliposomes. In the presence of symmetrical buffered solution and oligonucleotide, curren t passed linearly over the range of holding potentials tested, Conduct ance was 10.4 +/- 0.4 picosiemens (pS) and reversal potential was 0.2 +/- 1.7 mV. There was no difference in channel conductance or reversal potential between phosphodiester and phosphorothioate oligonucleotide s. Ion-substitution experiments documented a shift in reversal potenti al only when a concentration gradient for oligonucleotide was establis hed, indicating that movement of oligonucleotide alone was responsible for current, Movement of oligonucleotide across the bilayer was confi rmed by using P-32-labeled oligonucleotides, Channel open probability decreased significantly in the presence of heparan sulfate, These stud ies provide evidence for a cell surface channel that conducts nucleic acids.