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Proceedings of the National Academy of Sciences of the United States of America


Geisel School of Medicine


Saccharomyces cerevisiae vacuole inheritance requires two low molecular weight activities, LMA1 and LMA2. LMA1 is a heterodimer of thioredoxin and protease B inhibitor 2 (IB2). Here we show that the second low molecular weight activity (LMA2) is monomeric IB2. Though LMA2 / IB2 was initially identified as a protease B inhibitor, this protease inhibitor activity is not related to its ability to promote vacuole fusion: ( i ) Low M r protease B inhibitors cannot substitute for LMA1 or LMA2, ( ii ) LMA1 and LMA2 promote the fusionof vacuoles from a strain that has no protease B, ( iii ) low concentrations of LMA2 that fully inhibit protease B do not promote vacuole fusion, and ( iv ) LMA1, in which is complexed with thioredoxin,is far more active than LMA2 / IB2 in promoting vacuole fusion and far less active in inhibiting protease B. These studies establish a new function for IB2.



Original Citation

Slusarewicz P, Xu Z, Seefeld K, Haas A, Wickner WT. I2B is a small cytosolic protein that participates in vacuole fusion. Proc Natl Acad Sci U S A. 1997;94(11):5582-5587. doi:10.1073/pnas.94.11.5582