TRANSPORT AND LOCALIZATION ELEMENTS IN MYELIN BASIC-PROTEIN MESSENGER-RNA

Myelin basic protein (MBP) mRNA is localized to myelin produced by oli godendrocytes of the central nervous system. MBP mRNA microinjected in to oligodendrocytes in primary culture is assembled into granules in t he perikaryon, transported along the processes, and localized to the m yelin compartment. In this work, microinjection of various deleted and chimeric RNAs was used to delineate regions in MBP mRNA that are requ ired for transport and localization in oligodendrocytes. The results i ndicate that transport requires a 21-nucleotide sequence, termed the R NA transport signal (RTS), in the 3' UTR of MBP mRNA. Homologous seque nces are present in several other localized mRNAs, suggesting that the RTS represents a general transport signal in a variety of different c ell types. Insertion of the RTS from MBP mRNA into nontransported mRNA s, causes the RNA to be transported to the oligodendrocyte processes, Localization of mRNA to the myelin compartment requires an additional element, termed the RNA localization region (RLR), contained between n ucleotide 1,130 and 1,473 in the 3' UTR of MBP mRNA. Computer analysis predicts that this region contains a stable secondary structure. If t he coding region of the mRNA is deleted, the RLR is no longer required for localization, and the region between nucleotide 667 and 953, cont aining the RTS, is sufficient for both RNA transport and localization. Thus, localization of coding RNA is RLR dependent, and localization o f noncoding RNA is RLR independent, suggesting that they are localized by different pathways.