Abstract
A novel 85-kD protein factor which interacts specifically with the 5'-transcribed spacer of rat ribosomal genes was identified using the gel mobility shift, DNase I protection and UV-crosslinking techniques. The binding site of the factor is located inside the 36 bp Alul-HindIII fragment of transcribed spacer, most probably in the region +94 to +115 with respect to the transcription initiation site. Factors giving very similar gel mobility shift patterns were also found in mouse and human cell extracts. Sequences resembling the binding site of this factor were revealed in corresponding regions of mouse and human ribosomal genes. The biological function of FTS remains to be elucidated.