N- and C-terminal vectors detect different interactions. Y2H screens of the four different vector combinations showing the differences on 3 mM (A) and 25 mM 3AT (B). The same bait, ORF19 (Uniprot accession P09248) was used as bait with N-terminally and C-terminally fused DNA-binding and activation domains and screened against a whole-genome array of Varicella Zoster Virus (VZV). The N-terminal bait and prey constructs (in pGBKT7g, pGADT7g, NN) show markedly different interaction patterns compared to the C-terminal constructs cloned into pGBKCg and pGADCg (CC). NC and CN combinations show yet different interactions. Preys are indicated by their ORF number, e.g. the bait ORF19 is the large ribonucleotide reductase (RNR) subunit which is known to interact with itself and the small RNR subunit (ORF18 = Uniprot P09247). Note that N and C labels near yeast colonies indicate N- and C-terminal protein fragments, not AD or DBD fusions (e.g. 18C and 18N are N- and C-terminal domains of ORF18). A complete list of interactions is provided in Additional file 1: Table S1. The sequences of all proteins are listed in Additional file 1: Table 4.