CELL CYCLE-DEPENDENT REGULATION OF THE CYCLIN B1 PROMOTER

Cyclin B1 mRNA expression varies through the cell cycle with its peak in G(2)/M. In cycling mammalian cells, its lowest level is in G(1) wit h a steady increase in S until a level 50-fold greater than that in G( 1) is reached. In order to characterize the transcriptional component to this variation in expression, we cloned the upstream region 872 bas e pairs upstream from the start site of the cyclin B1 gene and have de monstrated that it confers cell cycle-dependent regulation onto two re porter genes, both chloramphenicol acetyltransferase and luciferase. I ts activity was 25-fold greater in G(2)/M than in G(1) in HeLa cells w ith intermediate activity in S. This cyclical activity could be seen w ith sequences encompassing only 90 base pairs upstream from the start site. Protein binding to this region was demonstrated using electropho retic mobility shift assays, and the binding profiles appeared to vary depending upon the phase of the cycle in which the extracts are made. Thus, transcriptional control plays an important role in determining cyclin B1 mRNA levels, and cell cycle-dependent activity is regulated through interactions with the region 90 bases upstream from the start site.