Role of multifunctional autonomously replicating sequence binding factor 1

Autonomously replicating sequence (ARS) binding factor 1 (ABF1) is an abundant DNA-binding protein that specifically recognizes the motif RTCRYN5ACG at many sites in the yeast genome, including promoter elements, mating-type silencers, and ARSs. Mutational analysis of these sites suggests that ABF1 is involved in constitutive and carbon source-regulated transcriptional activation, transcriptional silencing, and ARS activity. To better assess the role of ABF1 in DNA replication and transcriptional control, temperature-sensitive lethal mutations in the ABFI gene were isolated. Several of the abfl(Ts) strains show rapid growth arrest at the nonpermissive temperature. At the semipermissive temperature, these strains show an ARS-specific defect in the mitotic stability of ARS-CEN plasmids, such that the abfl mutants show defects in ARS function identical to those of mutants bearing the mutations in the cis-acting ABF1 binding sites analyzed previously by numerous investigators. Flow cytometric analysis and in vivo DNA labeling experiments on an ax-factor synchronized abfl(Ts) strain showed that at the nonpermissive temperature, these cells fail to progress efficiently from G1 through S phase and synthesize DNA at 25 % of the level seen in the isogenic ABFI strain. RNA synthesis is also reduced in the abfl(Ts) strains. In addition, transcriptional activation by an ABFI binding site upstream activation sequence is completely defective in an abfl(Ts) strain at the semipermissive temperature. These phenotypes provide evidence that the same protein, ABF1, functions in the initiation o