Although a number of different proteins have been implicated in linking transported and translationally controlled mRNAs to microtubules, only a few have been shown to bind directly to microtubules. Previous studies have shown that an RNA-binding activity specific for sequences present in the 3′ UTRs of a number of different mRNAs, including Prm2 and Tau, can be pelleted when protein extracts enriched for this RNA-binding activity are added to preassembled bovine brain microtubules. We have shown that SPNR can be pelleted with testis microtubules in a taxol-dependent manner. In addition, a His-tagged version of SPNR produced in bacteria behaves similarly to the endogenous protein, also pelleting with microtubules through multiple rounds of purification.
This E. coli-produced protein can also be pelleted with MAP-free bovine brain microtubules, an association that is salt sensitive. Since SPNR can be pelleted with microtubules in the absence of other MAPs, this experiment suggests that SPNR itself is a bona fide MAP. antibiotics levaquin
SPNR is a member of the double-stranded RNA-binding protein family that includes Drosophila Staufen and murine PRBP.