A chromatin acceptor protein for the avian oviduct progesterone receptor (PR), termed receptor binding factor 1 (RBF-1), has recently been shown to (1) be a component of the nuclear binding sites (acceptor sites) for PR and (2) generate high-affmity binding sites (termed the RBF-1 class of sites) on avian genomic DNA [Schuchard et al. (1991) Biochemistry 30, 4535-4542]. A second class of sites and its associated protein (termed RBF-2) were also identified. This paper demonstrates that RBF-1 and also the PR nuclear binding sites are localized in the oviduct nuclear matrix. RBF-1 is found in abundance in the nuclear matrix of liver but only in traces in the nuclear matrix of spleen. Extraction of the nuclear matrix with 4.0 M Gdn-HCl results in the complete removal of RBF-1 as occurs with whole chromatin. Interestingly, a second class of specific PR binding, termed RBF-2, remains on the nuclear matrix after the removal of all RBF-1. Southern blot analysis indicates that the nuclear matrix DNA contains sequences homologous with the 5′-flanking domains of the rapidly steroid regulated c-myc and c-jun protooncogenes and the β-actin gene, but not genomic sequences of the late sex steroid regulated gene, ovalbumin, or the α-actin gene. A specific, small region in the 5′-flanking domain of the c-myc gene appears to be associated with the nuclear matrix. Southwestern blot analysis using partially purified RBF-1 shows a marked affinity and specificity of the RBF-1 for the nuclear matrix DNA. These data support a direct action of progesterone on the rapidly regulated nuclear matrix protooncogenes. The possibility of an indirect action on late-regulated genes such as ovalbumin is discussed.
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