Proteins Required for DNA Replication

Two questions arise in separating the two strands of the original DNA so that it can be replicated. The first is how to achieve continuous unwinding of the double helix. This question is complicated by the fact that prokaryotic DNA exists in a supercoiled, closed-circular form (see Tertiary Structure of DNA Supercoiling in Section 9.3). The second related question is how to protect single-stranded stretches of DNA that are exposed to intracellular nucleases as a result of the unwinding. 

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The proliferation of cytotoxic T-cells is markedly impaired upon infection with a newly discovered human immunodeficiency virus, designated HIV-V. The defect has been traced to the expression of a viral-encoded enzyme that inactivates a host-ceU nuclear protein required for DNA replication. Which protein is a potential substrate for the viral enzyme ... 

Once active Cln3-CDK complexes accumulate in mid-late Gi, they phosphorylate and activate two transcription factors that stimulate expression of Clnl and Cln2, of enzymes and other proteins required for DNA replication, and of the S-phase B-type cyclins Clb5 and Clb6. 

In the decade following the description of Okazaki fragments, a combination of biochemical and genetic approaches led to the isolation and characterization of a large set of proteins required for DNA replication. The first class of enzymes to be described were the DNA polymerases. Table 22.1 lists the properties of the sev-... 

Multiple proteins are required for DNA replication at a replication fork. These include DNA polymerases, single-strand DNA binding proteins, helicases, primase, topoisomerases, and DNA ligase. Some of these are multisubunit protein complexes. 

Abstract. In eukaryotic cells, replicated DNA molecules remain physically connected from their synthesis in S phase until they are separated during anaphase. This phenomenon, called sister chromatid cohesion, is essential for the temporal separation of DNA replication and mitosis and for the equal separation of the duplicated genome. Recent work has identified a number of chromosomal proteins required for cohesion. In this review we discuss how these proteins may connect sister chromatids and how they are removed from chromosomes to allow sister chromatid separation at the onset of anaphase. 

Many proteins are required for DNA synthesis and chromosomal replication. These include polymerases helicases, which unwind the parental duplex enzymes that fill in the gaps and join the ends in the case of lagging-strand synthesis enzymes that synthesize RNA primers at various points along the DNA tem-... 

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