Biochemical characterization of INTS3 and C9ORF80, two subunits of hNABP1/2 heterotrimeric complex in nucleic acid binding

Human nucleic acid-binding protein 1 and 2 (hNABP1 and hNABP2, also known as hSSB2 and hSSB1 respectively) form two separate and independent complexes with two identical proteins, integrator complex subunit 3 (INTS3) and C9ORF80. We and other groups have demonstrated that hNABP1 and 2 are single-stranded (ss) DNA- and RNA-binding proteins, and function in DNA repair; however, the function of INTS3 and C9OFR80 remains elusive. In the present study, we purified recombinant proteins INTS3 and C9ORF80 to near homogeneity. Both proteins exist as a monomer in solution; however, C9ORF80 exhibits anomalous behavior on SDS–PAGE and gel filtration because of 48% random coil present in the protein. Using electrophoretic mobility shift assay (EMSA), INTS3 displays higher affinity toward ssRNA than ssDNA, and C9ORF80 binds ssDNA but not ssRNA. Neither of them binds dsDNA, dsRNA, or RNA : DNA hybrid. INTS3 requires minimum of 30 nucleotides, whereas C9OFR80 requires 20 nucleotides for its binding, which increased with the increasing length of ssDNA. Interestingly, our GST pulldown results suggest that the N-terminus of INTS3 is involved in protein–protein interaction, while EMSA implies that the C-terminus is required for nucleic acid binding. Furthermore, we purified the INTS3–hNABP1/2–C9ORF80 heterotrimeric complex. It exhibits weaker binding compared with the individual hNABP1/2; interestingly, the hNABP1 complex prefers ssDNA, whereas hNABP2 complex prefers ssRN...
Source: Biochemical Journal - Category: Biochemistry Authors: Tags: Research Articles Source Type: research