Studies have been initiated to identify the protein component(s) which interact with the β regulatory region of the mouse ribosomal protein L32 gene promoter. By the combined use of the mobility shift assay and UV cross-linking, a factor specific for the upstream transcriptional control sequence of the β region of the ribosomal protein L32 promoter has been detected in mouse L1210 nuclear extracts. A mutation (GT→TC at −71 to −70) in this sequence eliminates the binding. β factor is identified as a 55 kDA polypeptide by UV cross-linking. Addition of excess β element (double-stranded oligonucleotide) to a cell-free transcription system reduces transcription of the ribosomal protein L32 gene. Our results provide evidence that the interaction between the β element and the β factor is involved in ribosomal protein L32 transcription.
