• An episomally replicating vector binds to the nuclear matrix protein SAF-A in vivo.

      Jenke, Bok Hee C; Fetzer, Christian P; Stehle, Isa M; Jönsson, Franziska; Fackelmayer, Frank O; Conradt, Harald; Bode, Jürgen; Lipps, Hans J; Institute of Cell Biology, Stockumer Strasse 10, University of Witten/Herdecke, D-58448 Witten. (2002-04)
      pEPI-1, a vector in which a chromosomal scaffold/matrix-attached region (S/MAR) is linked to the simian virus 40 origin of replication, is propagated episomally in CHO cells in the absence of the virally encoded large T-antigen and is stably maintained in the absence of selection pressure. It has been suggested that mitotic stability is provided by a specific interaction of this vector with components of the nuclear matrix. We studied the interactions of pEPI-1 by crosslinking with cis-diamminedichloroplatinum II, after which it is found to copurify with the nuclear matrix. In a south-western analysis, the vector shows exclusive binding to hnRNP-U/SAF-A, a multifunctional scaffold/matrix specific factor. Immunoprecipitation of the crosslinked DNA-protein complex demonstrates that pEPI-1 is bound to this protein in vivo. These data provide the first experimental evidence for the binding of an artificial episome to a nuclear matrix protein in vivo and the basis for understanding the mitotic stability of this novel vector class.
    • NRF IRES activity is mediated by RNA binding protein JKTBP1 and a 14-nt RNA element.

      Reboll, Marc René; Oumard, André; Gazdag, Aniko Carla; Renger, Isabelle; Ritter, Birgit; Schwarzer, Michael; Hauser, Hansjoerg; Wood, Monika; Yamada, Michiyuki; Resch, Klaus; et al. (2007-08)
      The mRNA of human NF-kappaB repressing factor (NRF) contains a long 5'-untranslated region (UTR) that directs ribosomes to the downstream start codon by a cap-independent mechanism. Comparison of the nucleotide (nt) sequences of human and mouse NRF mRNAs reveals a high degree of identity throughout a fragment of 150 nt proximal to the start codon. Here, we show that this region constitutes a minimal internal ribosome entry segment (IRES) module. Enzymatic RNA structure analysis reveals a secondary structure model of the NRF IRES module. Point mutation analysis of the module determines a short, 14-nt RNA element (nt 640-653) as a mediator of IRES function. Purification of IRES binding cellular proteins and subsequent ESI/MS/MS sequence analysis led to identification of the RNA-binding protein, JKTBP1. EMSA experiments show that JKTBP1 binds upstream to the 14-nt RNA element in the NRF IRES module (nt 579-639). Over-expression of JKTBP1 significantly enhances activity of the NRF IRES module in dicistronic constructs. Moreover, siRNA experiments demonstrate that down-regulation of endogenous JKTBP1 decreases NRF IRES activity and the level of endogenous NRF protein. The data of this study show that JKTBP1 and the 14-nt element act independently to mediate NRF IRES activity.