The availability of the sequenced human genome now enables the critical pursuit of the function of all proteins.Proteins act together as molecular machines and understanding protein interactions is key to elucidate their function.Protein microarrays have demonstrated their utility to characterize protein interactions at the proteome scale.Nucleic Acid Programmable Protein Array (NAPPA),revolutionized protein arrays by simplifying the production of microarrays.In NAPPA method full length cDNAs corresponding to the proteins of interest are printed on the microarrays and then transcribed/translated in situ at the time of assay.