MIDA1 was reported as a protein that can associate with Id1. Its N-terminus has homology to Z-DNA binding protein, Zuotin, that contains DnaJ motif, considered to interact with Hsp70s, and Id binding domain. In the present study, we found that MIDA I stimulates the transcription of the co-transfected genes. This stimulation was independent of promoter specificity because it was observed in various transfected genes. MIDA1 enhanced formation of DNA-protein complexes with E-box or TATA box without its direct binding to DNA. Analysis with deletion mutants of MIDA I showed that the short protein fragment containing DnaJ motif within Zuotin homology region is sufficient for the stimulation of transcription and we demonstrated that MIDA1 associates with Hsp70. These data suggest involvement of MIDA I in the stimulation of transcription in concert with Hsp70/Hsc70 molecular chaperones, thus providing a link between Hsp70/Hsc70 molecular chaperones and components of the transcriptional machinery. (C) 2004 Elsevier Inc. All rights reserved.