Genome-Wide Analysis of Protein-Protein Interactions Using a Two-Hybrid Array: Amplification of ORFs This protocol describes the first step in constructing an array: amplification of the predicted ORFs that are to be included in the array. Gene-specific primers containing vector-specific flanking sequences that facilitate recombinational cloning are used to amplify each ORF. A secondary amplification can be used to extend the length of the homologous vector sequence flanking the ORF.