The invention relates to methods of making modular chimeric protein expression products and compositions utilized in the methods. In particular, the invention relates to sequential, directional cloning of polynucleotides encoding polypeptide modules. Each clonable element or module contains an open reading frame of interest flanked by predetermined restriction sites. The methods include using modules and vectors containing these modules as starting materials for recombinant DNA techniques. One advantage of the invention is that it allows for many variations of fusion proteins to be made quickly and easily without needing to design and evaluate each subsequent cloning step.
