Cloning of a cDNA Encoding a Novel Importin-α Homologue, Qip1: Discrimination of Qip1 and Rch1 from hSrp1 by Their Ability to Interact with DNA Helicase Q1/RecQL

Abstract We isolated two cDNA clones encoding human proteins which interact with DNA helicase Q1/RecQL, a human homologue of Eschelichia coli RecQ protein, by two-hybrid screening. One of these proteins, named Qip1, was a novel protein homologous to the nuclear localization signal (NLS) receptor importin-α, and the other was the known protein Rch1, which is also a homologue of importin-α. DNA helicase Q1 in human cell lysates was coprecipitated with bacterially expressed Qip1 and Rch1 fused with glutathione- S -transferase with glutathione Sepharose beads, confirming the interaction between these proteins and DNA helicase Q1. Two-hybrid experiments revealed that Qip1 interacted with the NLS of SV40 T antigen similar to Rch1 and hSrp1. In addition, interaction of the putative NLS in DNA helicase Q1 with Qip1 and Rch1 but not with hSrp1 was confirmed by the two-hybrid system.