The use of liposomes for constructing cell models.

We illustrate here in a form of a short review some of the work developed in our and other groups aiming at performing inside liposomes enzymatic reactions relevant for the origin of life. The work on giant vesicles will not be considered here. The long-range goal of our work with SUVs or LUVs (small unilamellar vesicles or large unilamellar vesicles) is the construction of a model minimal cell. By this we mean a cell-like system containing the minimal and sufficient number of macromolecular components for expressingsome of the basic functions of a living cell- such as protein biosynthesis, growth and self-reproduction, homeostasis based on a primitive metabolism. We begin describing a POPC liposomal system containing some of the enzymes of the salvage cycle for the synthesis of lecithin; then vesicles containing the nucleotide phosphorylase enzyme for the polymerisation of ADP into poly(A); an oleate self-reproducing vesicular system which hosts Qβ replicase for the replication of a RNA template; a POPC systems (POPC = 1-palmitoyl-2-oleoyl-sn-phosphatidylcholine) hosting the elements for a polymerase chain reaction; and finally the attempts to organize inside liposomes the ribosomal system capable of the synthesis of poly(phenylalanine). This analysis of published work will be followed by the description of novel work aimed at expressing a protein (green fluorescent protein) inside liposomes. The possible development of this work and its limits will be discussed.