Moving mRNAs through cytoplasm

Moving mRNAs through cytoplasm AINGER,K. et al (1993) Transportand localizationof exogenousmyelin basic protein mRNAmicmtnjected into oligodendrocytesJ. Cell Biol. 123, 431-441 Some mRNAs localize to specific areas of the cytoplasm for translation, thereby contributing to the distribution of proteins to different regions of the cell; for example, the localization of mRNA for regulatory prote.ns to the posterior or anterior region of the Drosophilo oocyte is the key to anterior-posterior specification in the fly. Although progress has been made in defining c/s-acting sequences required for mRNA localtzation within the cytoplasm, the underlying mechantsms remain un-

clear. This paper by Atnger et al now provides evtdence for the directional movement of mRNA encodtn~;myelin basic protein (MBP) along ohgodendrocyte processes, thus arguing against models that invoke mRNA diffusion and subsequenttrapping. In this study, the authr~rs used time-lapse confocal microscopy to follow the fate of fluorescently labelled mRNA micromjected into the cell body of living oligodendrocytes m culture Like the endogenous mRNA, the microinjected mRNA

forms granules tn the penkaryon, perhaps representing ribonucleoprotein complexes, and these subsequently show sustained anterograde mobon at 0.2 pms-1 along the process to the cell periphery. The granules appear to be associated with the cytoskeletal matrix. One obvious possibility is that the granules are translocated along microtubules of the process by motor proteins - but the details of how the granules move are still at the intriguing speculativestage

Membrane-specific tags for vesicle docking? AALTO, M. K., RONNE, H. and KER,~NEN,S. (1993) YeastsyntaxinsSsolp and Sso2pbelong to a family of relatedmembraneproteins that function in vestculartransport EMBO]. 12, 4095-4104

This paper describes the isolation of two closely related yeast genes S.~O! and S502 - whose products are together required for the transport of secretory proteins from the Golgl complex to the plasma membrane. The genes were isolated as multicopy suppressors of late-acting sec mutations. Ssolp and Sso2p, which are 72% identical In sequence, ar~ small proteins with a hydrophilic N-terminus, and a C-terminal hydrophobic tail thought to serve as a membrane anchor.

Sequence data show that Ssolp and Sso2p are members of a family of related proteins thought to be revolved in determining the specificity of Individual intracellular transport steps. These include yeast SedSp (required for ER-to-Golgl transport), yeast Pep12p (Involved in Golgl-tovacuole transport) and the mammalian syntaxlns A and B (thought to be involved in the docking of synaptlc vesicles to the plasma membrane). In fact, sequence similarities suggest that Ssolp and

Sso2p are yeast homologues of the syntaxins. Thus yeast and mammalian syntax. ins could act as plasma-membrane. specific tags to allow targeting of specific Golgi-derived vesicles to the plasma htembrane, while other members of the family could serve to label the other target mem. branes. An interesting problem that remains to be resolved is how these protein tags are themselves targeted to the correct membrane compartment.

CELLBIOLOGYTRENDS Some recent Trends articles of interest to cell biologists:

DNA damage and DNA.activated protein kinase Carl W. Anderson Trends in Biochemical Sciences 18, 433-437

Thinking about genetic redundancy James H. Thomas Trends in Genetics 9, 395-398

Intramolecular chaperones and protein folding U. Shinde and M. Inouye Trer,d; in Biochemical Sciences18, 442-446

Arabidopsis as a model host for studying plant-pathogen interactions B. Mauch-Mani and A. J. Slusarenko Tzends in Microbiology 1,265-269

Conservation and reiteration of a kinase cascade Aaron M. Neiman Trends in Genetics 9, 390-394

The distribution of myelin basic protein mRNAs within myelinating oligodendrocytes P. J. Brophy, G. L. Boccaccioand D. R. Caiman Trends in Ne~Jrosciences16, 515-521

TRENDSIN CELLBIOLOGYVOL 4 JANUARY1994

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