DNA Replication by Herpes Simplex Virus 1 Type

Document Type:Thesis

Subject Area:Chemistry

Document 1

Synthesis of leading and lagging, in trombone DNA replication model, is accompanied by making loops of strands that lag back to the fork. This is the site of synthesis for strands of lagging and leading in cycles in form of fragments that are short, called Okazaki fragments. They have sizes that vary from five hundred to six thousand nucleotides that are present in the prokaryotic systems that are well characterized (Voyles 132). Background to the Study In Vitro, deoxyribonucleic acid is replicated by proteins that have been encoded using herpes simplex virus 1 type. It is among the nine different herpes virus that infect humans. There was a correlation of these loop’s frequency with the deoxyribonucleic acid fraction that underwent fragment synthesis (Kornberg et al 42).

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The authors of this research were much interested in reconstituting replication by use of purified proteins. They used a deoxyribonucleic acid with synthetic seventy base mini-circle as the template. This 70-base mini-circle was basically a partial circle of dsDNA containing forty based SS 5’-tails needed for efficient binding and unwinding as well as a 20-base gap of leading strand that provides a site necessary for replisome assembling. The Leading strands of ten thousand nucleotides and fragments of Okazaki approximately 3,000 nucleotides in length were observed. Small circular deoxyribonucleic acid having displaced forks that are essential for providing rolling templates in circle replication can be used to study the basic structure of replication forks. Cells extracts infected with herpes simplex virus 1 on plasmid deoxyribonucleic acid substrates has been used to reconstitute rolling circle replication in vitro (Kornberg et al 52).

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Illustration of robust replication of rolling circle is an important step in understanding replication of HSV-1. This is usually accomplished using purified proteins of herpes simplex virus 1 that have been coupled with analysis of EM aimed at determining if its replication mode is in conformity with the descriptions in the systems of vitro T7 and T4. The diagram below illustrates a typical trombone cycle (Kornberg et al 56-57). The 90-nt oligonucleotide 5’ was used to anneal the mini-circle, providing a template strand for synthesis of lagging strand (Kornberg et al 67). The mixture pf the replication mixture that was contained in the 40 NM mini-circle and the alkaline agarose gel analyzed was included for purposes of monitoring the leading strand and also for synthesis of the lagging strand.

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The researchers incubated the reaction mixtures for around thirty and sixty minutes, stopping at final concentration of 0. 1 M just before the alkaline agarose gel electrophoresis (EM). The loading buffer of alkaline agarose was then added to the reactions that had already stopped, producing a final concentration of fifty millimeters of sodium hydroxide, four percent glycerol, 0. 6 percent of glutaraldehyde for approximately five minutes at room temperature. They were also chromatographed through 2 milliliters columns of six percent beads of agarose. The researchers then adsorbed the samples into thin supports of carbon in 2 mm spermidine. They were washed and dried using air. The products of the deproteinized reaction were visualized by treating the samples with proteinase K at fifty five degrees Celsius for sixty minutes.

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The amount of synthesis as well as the length of the replication increased over time. The products of the leading strand exceeded 20,000nt at the time point of sixty minute. This indicated that every mini circle that was active had been replicated over three hundred rounds. Length of products of the lagging strand was ranging between six hundred to nine thousand nucleotides after sixty minutes (Kornberg et al 73). They were shorter than the leading strand products, just as expected. However, the synthesis of the leading strand were barely impacted by the higher saturated concentrations of ICP8 (Kornberg et al 77). It was observed that the NTPs affected the production of both the lagging and leading strands. This synthesis highly depended on concentration of the NTPs.

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Okazaki fragment synthesis was initiated after only forty five minutes of incubation. However, there were 10,000nt long strands that were already present after the thirty minutes. There were large replisomes at one end of deoxyribonucleic acid products. These often featured a loop of DNA with a size reflecting the growth of Okazaki fragments. This provides the first evidence that trombone mechanism is capable of operating in the system of eukaryotic viral replication (Goldstein 52-53). New Information Provided by Researchers The deoxyribonucleic acid of the mini circle that is used in this study has many merits. Its comparison with plasmids of big sizes makes an allowance for the use of forks with high concentration. These results are essential in providing a basis for studies in future using EM, methods of single molecule as well as other various approaches for making further investigations of the DNA replications catalyzed by herpes simplex virus 1 (Brown and Alasdair 175-177).

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