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Science  05 Apr 2002:
Vol. 296, Issue 5565, pp. 15
DOI: 10.1126/science.296.5565.15c

During differentiation of professional secretory cells such as those in the pancreas or the liver, synthesis of the machinery of the secretory pathway—and in particular the rough endoplasmic reticulum (ER), which is the site of secretory protein synthesis—is dramatically increased. One of the machine parts is the mammalian ER protein p180, which serves as a receptor that binds the ribosome (the core of the protein synthesis machinery).

Heterologous expression of p180 in yeast induces proliferation of ER membranes and increases the capacity of the secretory pathway. Hyde et al. find that, contrary to expectations, these effects did not involve an induction of the unfolded protein response pathway or an increase in transcription of secretory machinery genes. Instead, it appeared that the lifetimes of messenger RNAs (mRNAs) encoding secretory pathway parts were extended, and this stabilization of mRNAs depended on their association with the ER. Whether this longevity is due to sequestration of the mRNAs from exonucleases or to interference with programmed RNA degradation will be of interest.—SMH

J. Cell Biol.156, 993 (2002).

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