Introduction

The recent advances in synthetic peptide technology have presented new opportunities to study plant signal transduction. In particular, the use of synthetic peptides has the advantage that relatively large quantities (10–100 mg) of pure site-specific reagents can be prepared with relative ease and can be utilised for a number of purposes. The most evident use is perhaps as synthetic antigens, where it is impossible or impracticable to isolate sufficient pure protein to permit immunisation. Such anti-peptide antibodies have proved extremely useful in identification of the plant homologues of their animal G protein (mainly Gα subunit) counterparts. However, there are other areas where synthetic peptides can be usefully employed. Important information concerning the substrate-specificity of protein kinases can be gained from observing the relative efficiency with which members of a series of peptides, each differing slightly in structure, can act as phosphate acceptors for the target kinase. Additionally, synthetic peptides can be used as direct mimics of protein structure in order to probe protein : protein interaction. For example, in our work we have utilised a peptide of moderate length (15 residues), whose sequence corresponds to a domain within the Gα subunit which is known to specify G-protein–receptor interaction, as an affinity ligand for receptor isolation. In other work, peptides that represent sections of the petD gene product have been used to delineate the domains of the petD protein, which may be important in LHC II kinase regulation.