Cell cycle control of the BN51 cell cycle gene which encodes a subunit of RNA polymerase III.

The BN51 cell cycle gene complements a temperature-sensitive cell cycle mutation of BHK-21 cells which leads to arrest in G1 at the nonpermissive temperature. Recent evidence indicates it encodes an essential subunit of RNA polymerase III. The BN51 gene is induced 4-fold 4-h after stimulation of quiescent, serum-starved fibroblasts with serum. This induction is abolished by the addition of the protein synthesis inhibitor cycloheximide. Nuclear runoff and transient transcription assays reveal a 2-3-fold increase in transcription in response to serum. There is a comparable 4-fold increase in BN51 protein synthesis following serum stimulation of quiescent fibroblasts. Loss of biologically active BN51 protein increases transcription from the BN51 promoter approximately 3-fold by transient transfection analysis. However, excess BN51 protein or the v-raf oncogene had no effect on transcription from the BN51 promoter in transient transfections. The pattern of transcription of the BN51 gene is similar to the delayed early response genes, which are induced several h after serum stimulation of quiescent cells.