Regions of human papillomavirus type 16 E7 oncoprotein required for immortalization of human keratinocytes.

Binding of the retinoblastoma gene product (pRB) by viral oncoproteins, including the E7 of human papillomavirus type 16 (HPV 16), is thought to be important in transformation of cells. One of the steps in transformation is the immortalization process. Here we show that mutations in E7 within the full-length genome which inhibit binding of pRB do not abrogate the ability of the HPV 16 DNA to immortalize primary human epithelial (keratinocyte) cells. A mutation in one of the cysteines of a Cys-X-X-Cys motif which is contained in the carboxy half of the E7 and is part of a zinc finger arrangement completely eliminates the ability of HPV 16 DNA to immortalize cells. The results indicate the importance of E7 in the immortalization of primary keratinocytes but suggest that the binding of pRB is not essential.     

dpa, a member of the MCM family, is required for mitotic DNA replication but not endoreplication in Drosophila.

We have isolated the Drosophila disc proliferation abnormal (dpa) gene, a member of the MCM family of DNA replication factors. Members of this family of proteins are required for DNA replication in yeast. A dpa null mutant dies during pupal stages because imaginal tissues necessary for the formation of the adult fly fail to proliferate normally. Beginning in late embryogenesis BrdU labeling reveals DNA replication defects in mitotically proliferating cells. In contrast, dpa is dispensable for endoreplication, a specialized cell cycle consisting of consecutive rounds of S phases without intervening mitosis. Our studies suggest an essential role for dpa in mitotic DNA replication but not in endoreplication. Thus, dpa is not a general replication factor but may play a specialized regulatory role in DNA replication.     

Molecular cloning of a family of retroviral sequences found in chimpanzee but not human DNA.

A number of retrovirus-like sequences have been cloned from chimpanzee DNA which constitute the chimpanzee homologs of the endogenous colobus type C virus CPC-1. One of the clones contains a nearly complete viral genome, but others have sustained deletions of 1 to 2 kilobases in the polymerase gene. The pattern of related sequences detected in other primate species is consistent with the genetic transmission of these sequences for millions of years. However, the appropriately related sequences have not been detected in human, gibbon, or orangutan DNAs. These results suggest either that this family of sequences has been deleted from humans, gibbons, and orangutans, or that the genes were recently acquired in the chimpanzee and gorilla lineages.