Selectively RNA interaction by a hnRNPA/B-like protein at presynaptic terminal of squid neuron

In previous works, we identified a RNA-binding protein in presynaptic terminal of squid neurons, which is likely involved in local mRNA processing. Evidences indicate this strongly basic protein, called p65, is an SDS-stable dimer protein composed of ~ 37 kDa hnRNPA/B-like subunits. The function of p65 in presynaptic regions is not well understood. In this work, we showed p65 and its subunit p37 are concentrated in RNA-enriched regions in synaptosomes. We performed in vitro binding studies with a recombinant protein and showed its propensity to selectively bind actin mRNA at the squid presynaptic terminal. Biochemical analysis using lysed synaptosomes suggested RNA integrity may affect p65 and p37 functions. Mass spectrometry analysis of oligo(dT) pull down indicated squid hnRNPA1, hnRNPA1-like 2, hnRNPA3 and ELAV-like proteins as candidates to interact with p65 and p37 forming a ribonucleoprotein complex, suggesting a role of squid hnRNPA/B-like proteins in site-specific RNA processing.