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As eukaryotic cells progress through the cell cycle, multiple genes involved in DNA replication and nucleotide metabolism are coordinately up-regulated shortly before or at the onset of DNA synthesis. These genes among others encompass histones, dihydrofolate reductase, thymidine kinase and synthase, proliferating cell nuclear antigen, topoisomerase II␣, and DNA polymerase ␣ (DPA) 1 /primase (1-3). A concordant up-regulation of the transcription factor Y-box protein 1 (YB-1) with topoisomerase II␣ and proliferating cell nuclear antigen has been previously reported (4); however, a direct involvement of YB-1 in the transcriptional control of the aforementioned genes has not been investigated. DPA is a key component of the chromosomal replication apparatus and is regarded as the principal polymerase involved in eukaryotic DNA replication (5). A role for DPA primase has been found in the checkpoint that couples S phase to mitosis (6). Furthermore, Wahl et al. (7) demonstrated a significant up-regulation of DPA gene transcription during the activation of quiescent (G 0 phase) to proliferating cells (G 1 /S phases). Steady state DPA mRNA levels, synthesis rates of nascent polymerase protein, and enzymatic activity all exhibit a substantial increase before the peak of in vivo DNA synthesis. The concerted increase of these three parameters is consistent with the regulation of this key DNA replication enzyme to a considerable extent at the transcriptional level. Studies performed by Wang and co-workers (7,8) demonstrated that in serum-deprived cells, DPA mRNA, protein, and in vitro activity levels are low, whereas serum addition leads to a coordinate increase in parallel with the onset of DNA synthesis. Prior analyses of the GC-rich TATA-less DPA promoter sequence for cis-acting elements identified a serum response element that is activated in NIH 3T3 cells (8). This element was mapped to sequences Ϫ65/Ϫ17 relative to the transcriptional start site. The 28-bp sequence Ϫ45/Ϫ17 includes an inverted CCAAT box and enhances transcription 10-fold in cycling cells when compared with the minimal activity construct Ϫ17/ϩ45 (8). Specific binding activities that trans-activate DPA gene transcription via this element include CTF1 (9) and CTF/NF-I (10). The importance of this sequence for DPA gene expression has also been demonstrated in the course of human cytomegalovirus infection. Human cytomegalovirus immediate-early protein 1 directly interacts with CTF1 and synergistically trans-activates DPA gene transcription via the inverted CCAAT box (9). Inverted CCAAT boxes also constitute binding sites for Ybox-binding proteins (11). YB-1 binds to DNA as well as RNA in a sequence-specific fashion and is implicated in the transcriptional regulation of a variety of genes (12). Depending on the cellular context, YB-1 may act either as a transcriptional activator or repressor, even of the same gene (13).Close inspection of the DPA gene sequences Ϫ45/Ϫ17 revealed the presence of an inverted CCAAT box on the opposite strand with an inverse rep...

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