1. Department of Laboratory Medicine,
2. Department of Cell and Organism Biology, and
3. Department of Clinical Sciences, Lund University, SE-22362 Lund, Sweden

Correspondence to: Gunnar Lindahl¹ Correspondence and requests for materials should be addressed to G.L. (Email: gunnar.lindahl@med.lu.se).

Abstract

All living cells require specific mechanisms that target proteins to the cell surface. In eukaryotes, the first part of this process involves recognition in the endoplasmic reticulum of amino-terminal signal sequences and translocation through Sec translocons, whereas subsequent targeting to different surface locations is promoted by internal sorting signals¹. In bacteria, N-terminal signal sequences promote translocation across the cytoplasmic membrane, which surrounds the entire cell, but some proteins are nevertheless secreted in one part of the cell by poorly understood mechanisms^{2, 3}. Here we analyse localized secretion in the Gram-positive pathogen Streptococcus pyogenes, and show that the signal sequences of two surface proteins, M protein and protein F (PrtF), direct secretion to different subcellular regions. The signal sequence of M protein promotes secretion at the division septum, whereas that of PrtF preferentially promotes secretion at the old pole. Our work therefore shows that a signal sequence may contain information that directs the secretion of a protein to one subcellular region, in addition to its classical role in promoting secretion. This finding identifies a new level of complexity in protein translocation and emphasizes the potential of bacterial systems for the analysis of fundamental cell-biological problems⁴.

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