The split-ubiquitin assay was based on the Dualmembrane kit3 (Dualsystems). The bait construct, pGAD-BT2-N-His33, expressing the CNV p33 replication protein has been described earlier [26] . The prey constructs were made by PCR amplification of individual genes using gene specific primers: #3957 (CCAGCTG-CAGTCACCACCAAGAAGAGTTG) / #4602 (CCAGCCAT-GGCCACCAAGAAGAGTTG) followed by digestion with EcoR1 and Nco1 for DED1 and #4312(CCAGGGATCCATGAC-TTACGGTGGTAGAG) / #4603 (CCAGCCATGGATAGT-TTGAACGACCTC), #4318 (CCAGGGATCCATGAGTCGC-TACGATAGCCG) / #4604 (CCAGCCATGGGCTCCACCC-TCTTCTGCTC) followed by digestion with BamH1 and Nco1 in the case of RH20 gene, respectively. Digested PCR products were fused to NubG at either the 59-or 39-termini (NubG-x and x-NubG) by cloning into pPRN-N-RE or pPRN-C-RE vectors [26] , respectively, using the same enzymes. Yeast strain NMY51 was co-transformed with pGAD-BT2-N-His33 and pPR-N-RE or one of the prey constructs carrying the cDNA for a given helicase and plated onto Trp 2 /Leu 2 synthetic minimal medium plates. Transformed colonies were picked with a loop, re-suspended in water, and streaked onto TLHA 2 (Trp 2 /Leu 2 /His 2 /Ade 2 ) plates to test for p33-helicase protein interactions as described [26] .