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Published May 1985 | Published
Journal Article Open

Invertase signal and mature sequence substitutions that delay intercompartmental transport of active enzyme


The role of structural signals in intercompartmental transport has been addressed by the isolation of yeast invertase (SUC2) mutations that cause intracellular accumulation of active enzyme. Two mutations that delay transport of core-glycosylated invertase, but not acid phosphatase, have been mapped in the 5' coding region of SUC2. Both mutations reduce specifically the transport of invertase to a compartment, presumably in the Golgi body, where outer chain carbohydrate is added. Subsequent transport to the cell surface is not similarly delayed. One mutation (SUC2-s1) converts an ala codon to val at position -1 in the signal peptide; the other (SUC2-s2) changes a thr to an ile at position +64 in the mature protein. Mutation s1 results in about a 50-fold reduced rate of invertase transport to the Golgi body which is attributable to defective signal peptide cleavage. While peptide cleavage normally occurs at an ala-ser bond, the s1 mutant form is processed slowly at the adjacent ser-met position giving rise to mature invertase with an N-terminal met residue. s2 mutant invertase is transported about sevenfold more slowly than normal, with no delay in signal peptide cleavage, and no detectable abnormal physical property of the enzyme. This substitution may interfere with the interaction of invertase and a receptor that facilitates transport to the Golgi body.

Additional Information

© 1985 by The Rockefeller University Press. Received for publication 17 November 1984, and in revised form 8 January 1985. We are especially grateful to Frank Masiarz (Chiron Corporation) for performing the Edman degradation analysis. We thank Will Rottman for his expert guidance in the DNA sequence analysis. I. Schauer was supported by a National Science Foundation predoctoral fellowship; S. Emr was supported by a postdoctoral fellowship from the Miller Institute for Basic Research in Science, University of California, Berkeley. This work was supported by grants from the National Institutes of Health (General Medical Sciences) and the National Science Foundation.

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