Drosophila behaviour/human splicing (DBHS) proteins are a family of RNA-binding proteins which mediate a host of functions relating to transcription regulation, transcriptional and post-transcriptional processing and nuclear export [1]. In humans, the protein family consists of three members: non-POU domain-containing octamer-binding protein (NONO), paraspeckle protein component 1 (PSPC1) and splicing factor proline/glutamine rich (SFPQ). Various studies and X-ray crystallographic structures show that DBHS proteins exist as obligate homodimers or heterodimers [1]. DBHS proteins exchange their dimerisation partner dynamically and their dimerisation state may have implications in various cellular context [1]. DBHS proteins also bind to the long non-coding RNA NEAT1 to form membraneless subnuclear bodies called paraspeckles which may mediate gene expression through the sequestering of RNA [2]. As many of the functions of DBHS proteins are mediated through RNA binding, knowledge of their RNA binding specificity could provide crucial information on their function.
We heterologously expressed and purified various combinations of DBHS protein dimers and probe their binding preferences to nucleotides by performing microscale thermophoresis experiments with homoribopolymers. While PSPC1 homodimer, NONO homodimer and PSPC1/NONO heterodimer all showed preference for uridine homoribopolymer, only NONO homodimer showed significant binding affinity for guanosine homoribopolymer. Next, we probed the binding affinity of the three DBHS dimers with two G-rich RNA sequences which are known to form G-quadruplexes. Again, only NONO homodimer interact with these G-rich RNA sequences with significant affinity. These results showed that the presence of PSPC1 in the DBHS dimer had attenuated the binding affinity of NONO to G-rich sequences. Further studies are planned to elucidate whether similar binding affinity characteristics are present in the homo- and hetero-dimer of SFPQ, the other member of the DBHS family.