Recent advances in the chemoselective ligation of peptides has greatly increased the range of useful proteins that can be produced in this manner. The adaptation of this procedure to facilitate the internal insertion of designer synthetic peptides between recombinantly derived protein fragments will be studied using a particular carrier protein. This protein spontaneously assembles into ordered, soluble, 27 nm particles containing 180 subunits. This structure has been demonstrated to be a superior carrier for exogenous, pathogen derived epitopes. The chemoselective insertion of peptide cassettes between recombinant N- and C-terminal fragments of the particulate carrier will be investigated to determine the feasibility of this directional, three-piece ligation procedure for generating novel fusion proteins harboring synthetic sequences. The physical, chemical and immunological integrity of the semisynthetic particles will be examined. A critical comparison of these data with those acquired for the entirely recombinant equivalents will enable an assessment of the utility of this approach. This work is expected to yield a versatile method for the introduction of B- and T-cell sites as well as novel amino acids or other chemical entities into a proven carrier protein that dramatically enhances immune responses to inserted sequences and conjugated haptens. Rapid production of analytical quantities of hybrid proteins will enable epitope scanning to identify useful antibody reactivities.