Polyamines have been identified to play a role in the transcription of various growth-related genes. The recently discovered polyamine responsive element and the associated trans-acting proteins involved in polyamine-regulated transcription have provided a model system for the study of the role of polyamines in transcription. Polyamine-modulated factor 1 (PMF-1) was identified as one of the transacting factors that binds to NF-E2 related factor-2 (Nrf-2) to regulate the transcription of spermidine/spermine N1-acetyltransferase (SSAT). The possibility that PMF-1 also binds to other proteins involved in transcriptional regulation cannot be ruled out. Using a yeast two-hybrid strategy, it was found that PMF-1 binds to a human homologue of the Arabidopsis COP9 signalosome subunit 7a (CSN 7) protein. In the present study, we describe human CSN 7, a 275-amino-acid- containing protein that may have a direct role in regulating gene expression. CSN 7 and PMF-1 bind to each other, as well as compete with each other for binding to Nrf-2. This competition for Nrf-2 binding and interaction with each other is implicated in the regulation of SSAT transcription. CSN 7 possesses a C-terminal coiled-coil domain similar to the domain that mediates the interaction between PMF-1 and Nrf-2, suggesting that coiled-coil domains also mediate the interaction between CSN 7 and PMF-1. Since CSN 7 does not contain a DNA-binding domain, its effects on transcription must occur in conjunction with binding to other proteins. The results presented here demonstrate that PMF-1 and Nrf-2 can act as protein partners of CSN 7.
- leucine zipper
Abbreviations used: BENSpm, N1,N11-bis(ethyl)norspermine; CSN 7, COP9 signalsome subunit 7a; EMSA, electrophoretic mobility-shift assay; IPTG, isopropyl β-d-thiogalactoside; Nrf-2, NF-E2 related factor-2; NBE, Nrf-2 binding element; Ni-NTA, Ni2+-nitrilotriacetate; ORF, open reading frame; PMF-1, polyamine-modulated factor 1; PRE, polyamine responsive element; SD-Trp, synthetic dextrose medium lacking tryptophan; SSAT, spermidine/spermine N1-acetyltransferase.
- The Biochemical Society, London ©2002