Helicase activities enzymes

Since the pioneering work of Kleymann et al. (2002), Betz et al. (2002), Baumeister et al. (2007), and Crute et al. (2002), who showed that compounds identified as inhibitors of the helicase-primase enzyme complex could alleviate herpesvirus-induced disease in animal models, the attention of researchers developing antiviral compounds has been drawn more and more towards the virus-encoded helicases, particularly those of Herpes viruses and of RNA viruses such as Hepatitis C Virus (HCV) and SAKS coronavirus (SARS-CoV). Enzyme activity is usually assayed by measuring NTPase activity in the presence of an appropriate nucleic acid co-substrate although, more recently, novel fiuorimetric and luminescence principles have been applied to the measurement of strand unwinding and/or translocation of the protein along the nucleic acid (Frick 2003, 2006). 

These studies [45] [47] suggest that specific protein-protein interactions between a single-stranded-DNA-binding protein and two replicative DNA-helicases allows substantial unwinding of substrates containing the major cisplatin lesion, but the mechanisms of stimulation of the helicases activities by the ICP8 protein appears to be different for the two enzymes. 

It requires helicase (bacterial enzyme has inherent helicase activity). 

The RNA helicase activity of the full-length NS3/4A enzyme (8) and of the NS3 C-terminal helicase domain has been demonstrated (10,11,17-19) by the unwinding of double-stranded RNA (dsRNA) molecules. The directionality of RNA helicase unwinding is 3 to 5 with respect to the template strand (8,19). Unlike most other helicases, the HCV NS3 helicase is capable of unwinding both RNA and DNA homoduplex and heteroduplex molecules (19). In common with other helicases, NS3 helicase requires divalent cations (Mg2+ or Mn2+) in conjunction with the hydrolysis of nucleoside triphosphates (NTPs) to provide the energy source for unwinding (11,12). 

To date, the most successful antiviral targets have been directed against viral-specific enzymes. Therefore, the ATPase and helicase activities of the El protein are attractive targets. Papillomavirus DNA replication may also be inhibited by compounds that interfere with the ability of El to bind DNA or to interact with the E2 protein. This chapter will describe a method to assay for specific El DNA binding and cooperative origin binding with the E2 protein and a method to transiently assay papillomavirus DNA replication. The methods described are for bovine papillomavirus type 1 (BPV-1), which has been the molecular prototype of the papillomaviruses. However, the methods can easily be adapted to assay for human papillomavirus replication. 

The NER pathway is also present in prokaryotic organisms, such as Escherichia coli, as well as in eukaryotes from yeast to mammals. Many of the basic steps of NER are evolutionarily conserved, including damage recognition and dual incisions to excise the lesion, helicase activity to displace the excised oligonucleotide and repair factors, and synthesis and ligation enzymes to seal the nick [19, 20], Nevertheless, the biochemical features in prokaryotes and eukaryotes are distinct. 

Assessment of the obstruction by TFIIH, unwinding of the DNA by helicase activity of TFIIH, and recruitment of appropriate repair enzymes... 

Correct answer = C. Fluoroquinolones, such as ciprofloxacin, inhibit bacterial DNA gyrase—a type II DNA topoisomerase. This enzyme catalyzes the transient breaking and rejoining of the phosphodiester bonds of the DNA backbone, to allow the removal of positive supercoils during DNA replication. The other enzyme activities mentioned are not affected. Primase synthesizes RNA primers, helicase breaks hydrogen bonds in front of the replication fork, DNA polymerase I removes RNA primers, and DNA igase joins Okazaki fragments. 

DNA helicases are a class of enzymes necessary for fundamental DNA transactions such as DNA replication, transcription, repair, and recombination. Moreover, among the components of the DNA replication, repair, recombination or transcription apparatus, the first that may encounter a site of DNA damage are the DNA helicases. Thus, a complete understanding of the effect of cisplatin lesions on DNA metabolism requires a biochemical analysis of their interaction with this class of proteins. At least three reports have investigated the effects of cisplatin intrastrand lesions on the activity of DNA helicases implicated either in repair or in recombination. 

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