CBP CYCA, A CCAAT-BINDING PROTEIN NECESSARY FOR ADHESION-DEPENDENT CYCLIN-A TRANSCRIPTION, CONSISTS OF NF-Y AND A NOVEL M-R-115,000 SUBUNIT/

Cells of most tissues, with the exception of hematopoietic cells, requ ire adhesion to an appropriate surface to grow. Cyclin A is needed for cell cycle progression at the G(1)-S transition, and appearance of cy clin A mRNA and protein in late G(1) has been shown to be dependent on adhesion-initiated signals in normal rat kidney fibroblasts. Previous ly, we have reported that the adhesion-dependent activation of cyclin A transcription in late G(1) is mediated by CBP/cycA (CCAAT-binding pr otein for cyclin A gene), a novel CCAAT-binding protein. Specific bind ing of CBP/cycA, a M-r 30,000/40,000/115,000 heterotrimeric protein co mplex, to the CCAAT element of the cyclin A promoter was detectable in growing but not in G(0)-arrested or nonadherent normal rat kidney cel ls. Here, me demonstrate that the M-r 30,000/40,000 subunits of CBP/cy cA are identical with NF-Y-A and NF-Y-B, the two subunits of NF-Y. In addition, we show that, aside from CBP/cycA, NF-Y itself also binds to the CCAAT element of the cyclin A promoter. But, whereas the binding of CBP/cycA is adhesion and cell cycle dependent and correlates with t he expression of cyclin A in late G(1) phase, NF-Y itself seems to bin d in a cell cycle-independent manner.