DIFFERENTIAL DEVELOPMENTAL EXPRESSION OF THE REPB AND REPD XERODERMA-PIGMENTOSUM RELATED DNA HELICASE GENES FROM DICTYOSTELIUM-DISCOIDEUM

DNA helicases are essential to many cellular processes including recom bination, replication and transcription, and some helicases function i n multiple processes. The helicases encoded by the Xeroderma pigmentos um (XP) B and D genes function in both nucleotide excision repair and transcription initiation. Mutations that affect the repair function of these proteins result in XP while mutations affecting transcription r esult in neurological and developmental abnormalities, although the un derlying molecular and cellular basis for these phenotypes is not well understood. To better understand the developmental roles of these gen es, we have now identified and characterized the repB and repD genes f rom the cellular slime mold Dictyostelium discoideum. Both genes encod e DNA helicases of the SF2 superfamily of helicases The repD gene cont ains no introns and the repB gene contains only one intron, which make s their genomic structures dramatically different from the correspondi ng genes in mammals and fish. However the predicted Dictyostelium prot eins share high homology with the human XPB and XPD proteins. The sing le copy of the repB and D genes map to chromosomes 3 and 1, respective ly, The expression of repB and D (and the previously isolated repE) ge nes during multicellular development was examined, and it was determin ed that each rep gene has a unique pattern of expression, consistent w ith the idea that they have specific roles in development. The pattern and extent of expression of these genes was not affected by the growt h history of the cells, implying that the expression of these genes is tightly regulated by the developmental program. The expression of the rep genes is a very early step in development and may well represent a key event in the initiation of development in this organism.