Question

Several distinct mechanisms for mRNA localization have been discovered. They all require specific sequences in the mRNA itself, usually in the 3’ untranslated region (UTR). Briefly outline three mechanisms by which cellular mRNAs might become localized in the cell

Answer 1

Studies in diverse systems such as oocytes, embryos, and somatic cells have indicated many potential mechanisms by which RNAs can be localized. These include the active directional transport of RNA on cytoskeletal elements, general degradation and localized RNA stability, random cytoplasmic diffusion and trapping, and vectorial transport from the nucleus to a specific target. A combination of mechanisms may be used to localize different RNAs; however, the most convincing evidence exists for the mechanisms of active directional transport on cytoskeletal elements and degradation combined with localized stability.

After the completion of transcription in the nucleus, majority RNAs exit through the nuclear pores into the cytoplasm and get translated. Some classes of RNA are targeted to specific regions within the cell or embryo and are not translated until they reach their final destination.

The cis-acting elements determine the initial steps in the localization process within the RNA. These signals usually located within the 3? UTR direct the binding of trans-acting factors to the RNA.

This influences the folding of the RNA into a specific spatial configuration facilitating the association of a series of other auxiliary proteins, producing a large ribonucleoprotein (RNP) transport particle. The RNA will be recognized through protein factors and associate it with the proper pathway or subcellular structure that will direct it to its proper destination.

Pathways utilize cytoskeletal machinery, and active transport mechanism involving a molecular motor that, along with adaptor proteins, will propel the mRNA. Once at its destination, it will anchor through a molecular anchor.