The asymmetric subcellular distribution of RNA molecules from their sites of transcription to specific compartments of the cell is an important aspect of post-transcriptional gene regulation. This involves the interplay of intrinsic cis-regulatory elements within the RNA molecules with trans-acting RNAbinding proteins and associated factors. Together, these interactions dictate the intracellular localization route of RNAs, whose downstream impacts have wide-ranging implications in cellular physiology. In this review, we examine the mechanisms underlying RNA localization and discuss their biological significance. We also review the growing body of evidence pointing to aberrant RNA localization pathways in the development and progression of diseases.Keywords: Cis-regulatory elements; RNA disease; RNA localization; RNA-binding proteinsThe asymmetric organization of cells is a pervasive feature that ensures the homeostasis of prokaryotic and eukaryotic organisms. This relies on the capacity of cells to organize their contents, including lipids, nucleic acids, and proteins, into specific subcellular structures and organelles. While much of this organization has been attributed to subcellular protein transport [1], a growing body of work indicates that the regulated localization of RNA molecules is also a key process observed across evolutionary timescales [2][3][4][5][6]. This form of post-transcriptional regulation where coding and noncoding RNA molecules actively associate with trans-acting partners, such as RNA-binding proteins (RBPs), serves to dictate both the function and intra-or extracellular destiny of the RNA. During RNA localization, cis-regulatory elements found within the RNA molecule, whether coding or noncoding, act as recognition sites for the recruitment of trans-acting RBPs, which dictate the intra-/extra-cellular fate of the RNA and, ultimately, its functional state. Over the years, the wide-ranging implications of RNA localization on cellular physiology have become apparent, affecting many aspects of cell organization and function. Indeed, RNA localization pathways have been linked to numerous important processes, including developmental patterning, cell polarity, spindle assembly, formation of nonmembranous compartments, localized translation, and cell motility [2][3][4][5][6].

Two Gram-negative, aerobic, non-motile, rod-shaped bacterial strains, FH13 T and FH23, representing a novel group of Rhizobium isolated from root nodules of Phaseolus vulgaris in Mexico, were studied by a polyphasic analysis. Phylogeny of 16S rRNA gene sequences revealed them to be members of the genus Rhizobium related most closely to 'Rhizobium anhuiense' CCBAU 23252 (99.7 % similarity), Rhizobium leguminosarum USDA 2370 T (98.6 %), and Rhizobium sophorae CCBAU 03386 T and others (j98.3 %). In sequence analyses of the housekeeping genes recA, glnII and atpD, both strains formed a subclade distinct from all defined species of the genus Rhizobium at sequence similarities of 82.3-94.0 %, demonstrating that they represented a novel genomic species in the genus Rhizobium. Mean levels of DNA-DNA relatedness between the reference strain FH13 T and the type strains of related species varied between 13.0¡2.0 and 52.1¡1.2 %. The DNA G+C content of strain FH13 T was 63.5 mol% (T m ). The major cellular fatty acids were 16 : 0, 17 : 0 anteiso, 18 : 0, summed feature 2 (12 : 0 aldehyde/unknown 10.928) and summed feature 8 (18 : 1v7c). The fatty acid 17 : 1v5c was unique for this strain. Some phenotypic features, such as failure to utilize adonitol, L-arabinose, D-fructose and D-fucose, and ability to utilize D-galacturonic acid and itaconic acid as carbon source, could also be used to distinguish strain FH13 T from the type strains of related species. Based upon these results, a novel species, Rhizobium acidisoli sp. nov., is proposed, with FH13 T (5CCBAU 101094 T 5HAMBI 3626 T 5LMG 28672 T ) as the type strain.