Novel 8-base pair sequence (Drosophila DNA replication-related element) and specific binding factor involved in the expression of Drosophila genes for DNA polymerase alpha and proliferating cell nuclear antigen.

Abstract:

Upstream regions containing a novel common 8-base pair (bp) palindromic sequence, 5'-TATCGATA (Drosophila DNA replication-related element (DRE)), are required for the high expression of Drosophila genes for DNA polymerase alpha and the proliferating cell nuclear antigen (PCNA) (an auxiliary protein for DNA polymerase delta). Three DREs and one DRE are present in the DNA polymerase alpha gene (nucleotides-217, -83, and -30 with respect to the transcription initiation site) and in the PCNA gene (nucleotide-100), respectively. Deletions or 2-bp insertional mutations of DRE sequences led to an extensive reduction of promoter activities of both genes. Chemically synthesized oligonucleotides containing DRE sequences greatly stimulated the activity of the heterologous promoter of the Drosophila metallothionein gene, in addition to the promoter of the PCNA gene, when they were placed upstream from these promoters in a normal or a reverse orientation. The stimulatory effect increased synergistically and depended on the number of DREs. DRE activated the promoter when placed within 1.4 kilobases upstream from the promoter, but was much less active when placed 2.5 kilobases or more apart from the promoter. Using a gel mobility shift assay method, we obtained evidence for a protein factor (DREF) in the nuclear extract of cultured Drosophila cells (Kc cells), and this factor specifically binds to DREs of both genes. DNase I footprinting analysis indicated that DREF binds to the 24-bp DRE region of the DNA polymerase alpha gene in which 8-bp palindromic sequences are centered. A UV cross-linking experiment revealed that a polypeptide of approximately 90 kDa in the nuclear extract interacts directly with the DRE sequence. Using DRE-conjugated latex particles, DREF was affinity-purified from the Kc cell nuclear extract. By comparing results obtained by SDS-polyacrylamide gel electrophoresis and gel mobility shift experiments, we concluded that DREF is associated with the 86-kDa polypeptide. On gel filtration chromatography, a single peak of DREF activity was recovered in fractions corresponding to a molecular mass of 170 kDa, and the 86-kDa polypeptide was detected only in the corresponding fractions; thus, active DREF is probably a homodimeric form of the 86-kDa polypeptide. DREF may play important roles in coordinating expressions of Drosophila DNA replication-related genes.

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