Use of a proteome strategy for tagging proteins present at the plasma membrane

A plasma membrane (PM) fraction was purified from Arabidopsis thaliana usin g a standard procedure and analyzed by two-dimensional (2D) gel electrophor esis. The proteins were classified according to their relative abundance in PM or cell membrane supernatant fractions. Eighty-two of the 700 spots det ected on the PM 2D gels were microsequenced. More than half showed sequence similarity to proteins of known function. Of these, all the spots in the P M-specific and PM-enriched fractions, together with half of the spots with similar abundance in PM fraction and supernatant, have previously been foun d at the PM, supporting the validity of this approach. Extrapolation from t his analysis indicates that (i) approximately 550 polypeptides found at the PM could be resolved on 2D gels; (ii) that numerous proteins with multiple locations are found at the PM; and (iii) that approximately 80% of PM-spec ific spots correspond to proteins with unknown function. Among the latter, half are represented by ESTs or cDNAs in databases. In this way, several un known gene products were potentially localized to the PM. These data are di scussed with respect to the efficiency of organelle proteome approaches to link systematically genomic data to genome expression. It is concluded that generalized proteomes can constitute a powerful resource, with future comp letion of Arabidopsis genome sequencing, for genome-wide exploration of pla nt function.