The many ways to cross the plasma membrane

The transfer into living cells of macromolecules, which monitor or modify molecule-specific intracellular processes, provides an efficient way to study the temporal and spatial regulation of protein systems that underlie basic cellular functions. Several methods have been developed for this purpose. Each of them has its characteristic advantages and disadvantages with respect to cell viability, transfer efficiency, general applicability, and technical requirements. We discuss current methodologies for the introduction of macromolecules, notably proteins, into cells in light of a new paper by Walev et al. (1) in a recent issue of PNAS in which a new protocol is provided for the reversible permeabilization of cells by using streptolysin-O. The function and interaction of many more novel proteins identified by the genome projects worldwide will have to be analyzed in the future. Therefore, transfer techniques that are easy to use, inexpensive, and suitable for automation such as the one described by Walev et al. (1) will become of superior importance. Worldwide genomic and cDNA sequencing projects are now identifying new molecules every day. The genomic sequences of the most widely studied species , Saccharomyces cerevisiae, Caenorhabditis elegans , and Drosophila melanogaster , have recently been completed. The full genomic sequence of Homo sapiens will become available soon. An enormous task, and a great challenge, will now be to relate these sequences to functional data that may subsequently open new avenues of research toward the cure of diseases. Together with the methodological progress made in the past two decades in expressing and manipulating cloned genes in the test tube, these sequence data provide us with the necessary molecular tools to understand the connectivity and spatial organization of protein systems in their native environment, the living cell. Common strategies in modern cell and molecular biology, which aim toward the identification of the role …