REPRESSION OF REGULATORY FACTOR FOR DROSOPHILA DNA REPLICATION-RELATED GENE PROMOTERS BY ZERKNULLT HOMEODOMAIN PROTEIN

The expression of the chloramphenicol acetyltransferase gene under con trol of the 1152-base pair 5'-flanking region (-1107 to +45 nucleotide positions with respect to the major transcription initiation site) of the Drosophila DNA polymerase alpha gene was repressed by cotransfect ion into Drosophila Kc cells with a zerknullt (zen)-expressing plasmid as previously observed with the proliferating cell nuclear antigen (P CNA) gene promoter. The expression of the zen resulted in reduction of the abundance of mRNA for the transfected chloramphenicol acetyltrans ferase gene and also mRNAs for both DNA polymerase alpha and PCNA. Res ults obtained using various deletion derivatives of the promoter regio n and chemically synthesized oligonucleotides of the DNA replication-r elated element (DRE), a positive cis-acting element found in both DNA polymerase alpha and PCNA genes, revealed that the DRE sequences are r esponsible to repression by Zen protein. The nuclear extract of Kc cel ls transfected by the zen-expressing plasmid contained lesser amounts of the DRE-binding factor (DREF) than that of untransfected or mutant zen-transfected cells. These results suggest that the Zen protein repr esses expression of DNA replication-related genes by reducing DREF, al though the detailed mechanism of the repression remains to be elucidat ed.