Saccharomyces cerevisiae vacuole inheritance requires two low molecular weight activities, LMA1 and LMA2. LMA1 is a heterodimer of thioredoxin and protease B inhibitor 2 (I2B). Here we show that the second low molecular weight activity (LMA2) is monomeric I2B. Though LMA2/I2B was initially identified as a protease B inhibitor, this protease inhibitor activity is not related to its ability to promote vacuole fusion: (i) Low Mr protease B inhibitors cannot substitute for LMA1 or LMA 2, (ii) LMA1 and LMA2 promote the fusion of 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 I2B is complexed with thioredoxin, is far more active than LMA2/I2B in promoting vacuole fusion and far less active in inhibiting protease B. These studies establish a new function for I2B.

• PMID: 9159115
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Journal Article | Research Support, Non-U.S. Gov't | Research Support, U.S. Gov't, P.H.S.

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Slusarewicz P, Xu Z, Seefeld K, Haas A, Wickner WT

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