The ubiquitous nature of the progesterone receptor binding factor‐1 (RBF‐1) in avian tissues

The avian oviduct receptor binding factor‐1 (RBF‐1) is a 10 kDa nuclear matrix protein that was originally identified through its ability to effect high affinity interaction of activated progesterone receptor (PR) with chromatin. In the present study, the RBF‐1 is shown to not be restricted to reproductive tissues (e.g., oviduct) but present in all avian tissues examined by Western blot analysis with a monoclonal antibody prepared against purified RBF‐1. The heart and pancreas had the highest and lowest RBF‐1 levels, respectively; the concentration ranging by ∼ 50‐fold in these tissues. The 10 kDa size of the RBF‐1 detected in all tissues suggests no significant tissue‐specific differences in the protein. This was consistent with the finding that purified hepatic and oviductal RBF‐1 have identical amino‐terminal sequence. Using a recently isolated cDNA to RBF‐1, the levels of RBF‐1 mRNA were found to correlate well with the ubiquitous presence of the protein as well as tissue‐specific differences in concentration. The presence of RBF‐1 in non‐progesterone responsive tissues suggests the possibility that RBF‐1 may not be specifically involved in PR‐DNA interactions but may play a more diverse role, possibly involving other steroid receptors such as the glucocorticoid receptor. © 1994 Wiley‐Liss, Inc.