We have previously identified a silencer (negative enhancer) in glutathione 
transferase P (GST-P) gene which is strongly and specifically induced during 
hepatocarcinogenesis of the rat. At least three trans-acting factors bind to 
multiple cis-elements located in this silencer. One of these factors, SF-B 
(Silencer Factor B) specifically binds to GPS1 (GST-P Silencer 1) and has been 
cloned by a Southwestern protocol. Analysis of DNA and deduced amino acid 
sequence reveals that SF-B clone is most likely identical to an IL-6 inducible 
trans-activator LAP/IL6-DBP. Binding efficiency of SF-B to GPS1 is 
indistinguishable from that to IL6-responsive element found in C-reactive 
protein gene. The possibility that SF-B/LAP/IL6-DBP functions as a dual positive 
and negative regulator is discussed.