Figure 1.

A model for the mutual dependence of amino-acid biosynthetic pathways between Buchnera and its host cell. Buchnera is located in a vacuole of the bacteriocyte. According to its gene repertoire, it is able to synthesize amino acids that are essential for the host organism (red). On the other hand, Buchnera appears to require external supply of several amino acids that are not essential to the host (blue). Among these amino acids are aspartate and glutamate (magenta), which, together with other amino-acid precursors, seem to be imported from the host cytoplasm by the endosymbionts in order to enable biosynthesis of the respective host-essential amino acids.