Helicase activities

Tai CL, Chi WK, Chen DS, Hwang LH (1996) The helicase activity associated with hepatitis C virus nonstructural protein 3 (NS3). J Virol 70 8477-8484 Tong X, Chase R, Skelton A, Chen T, Wright-Minogue J, Malcolm BA (2006) Identification and analysis of fitness of resistance mutations against the HCV protease inhibitor SCH 503034. Antiviral Res 70 28-38... 

Townsend L, Devivar R, Turk S, Nassiri M, Drach J (1995) Design, synthesis, and antiviral activity of certain 2,5,6-trihalo-l-(beta-d-ribofuranosyl)benzimidazoles. J Med Chem 38 4098 105 Turlure F, Devroe E, Silver PA, Engelman A (2004) Human cell proteins and human immunodeficiency virus DNA integration. Front Biosd 9 3187-3208 Umehara T, Fukuda K, Nishikawa F, Kohara M, Hasegawa T, NisUkawa S (2005) Rational design of dual-functional aptamers that inhibit the protease and helicase activities of HCV NS3. J Biochem 137 339-347... 

Two proteins are initially involved in the nonho-mologous rejoining of a ds break. Ku, a heterodimer of 70 kDa and 86 kDa subunits, binds to free DNA ends and has latent ATP-dependent helicase activity. The DNA-bound Ku heterodimer recruits a unique protein kinase, DNA-dependent protein kinase (DNA-PK). DNA-PK has a binding site for DNA free ends and another for dsDNA just inside these ends. It therefore allows for the approximation of the two separated ends. The free end DNA-Ku-DNA-PK complex activates the kinase activity in the latter. DNA-PK reciprocally phos-phorylates Ku and the other DNA-PK molecule, on the opposing strand, in trans. DNA-PK then dissociates from the DNA and Ku, resulting in activation of the Ku helicase. This results in unwinding of the two ends. The unwound, approximated DNA forms base pairs the extra nucleotide tails are removed by an exonucle-... 

The vulnerable point for insulin-mediated regulation of translation is the initiation factor eIF-4E. This factor binds specifically to the 5 -cap structure of mRNA and is part of a larger complex, termed eIF-4F. A further component of eIF-4F is the eIF-4A protein, which possesses helicase activity. The binding of eIF-4E to the cap structure is necessary for the association of the 40S subunit with the 5 -end of the mRNA and for... 

FIGURE 25-12 Model for initiation of replication at the E. coli origin, oriC. (D About 20 DnaA protein molecules, each with a bound ATP, bind at the four 9 bp repeats. The DNA is wrapped around this complex. The three A=T-rich 13 bp repeats are denatured sequentially. (3) Hexamers of the DnaB protein bind to each strand, with the aid of DnaC protein. The DnaB helicase activity further unwinds the DNA in preparation for priming and DNA synthesis. 

The p-dependent terminators lack the sequence of repeated A residues in the template strand but usually include a CA-rich sequence called a rut (rho rhilization) element. The p protein associates with the RNA at specific binding sites and migrates in the 5 —>3 direction until it reaches the transcription complex that is paused at a termination site. Here it contributes to release of the RNA transcript. The p protein has an ATP-depend-ent RNA-DNA helicase activity that promotes translocation of the protein along the RNA, and ATP is hydrolyzed by p protein during the termination process. The detailed mechanism by which the protein promotes the release of the RNA transcript is not known. 

TFIIE 2 34,000, 57,000 Recruits TFIIH hasATPase and helicase activities... 

TFIIH 12 35,000-89,000 binding of Pol II to nonspecific DNA sequences Unwinds DNA at promoter (helicase activity) ... 

ATP-dependent helicase activities that open up DNA for transcription (see Chapter 28, Section B). 

Rho and other termination factors. Termination proteins can also react with specific regions of DNA or of an RNA transcript to terminate transcription.183 The best known termination factor is the rho protein a hexamer of 45-kDa subunits. It interacts with transcripts at specific termination sequences, which are often C-rich, and in a process accompanied by hydrolysis of ATP causes release of both RNA and the polymerase from the DNA.192193 Additional E. coli proteins, products of genes nus A and nus G, cooperate with the rho factor at some termination sequences.194-196c The rho hexamer is a helicase that moves along the RNA transcript in the 5 —> 3 direction driven by ATP hydrolysis. If it locates an appropriate termination signal, it may utilize its helicase activity to uncoil the DNA-RNA hybrid segment within the transcription bubble (Fig. 28-4).197 198b... 

Im, D. S. and Muzyczka, N. (1990). The AAV origin binding protein Rep68 is an ATP-dependent site-specific endonuclease with DNA helicase activity. Cell 61, 447 157. 

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. 

The discoveries of Csp s and trigger factor may represent the tip of a large iceberg. In view of the pervasive effects of low temperature on the structures of all classes of macromolecules, it is reasonable to conjecture that many more types of proteins will be discovered whose roles are to offset the effects of cold shock on the cell. Some of these molecules may be expressed constitutively and may be part of the normal machinery of the cell. For example, certain ribosomal proteins are thought to function as RNA chaperones, and if present in sufficient amounts, these proteins may allow the cell to cope with the effects of cold shock on the structures of certain classes of RNAs. In yeast, a constitutively expressed ribosomal protein has helicase activity, and mutation in the gene encoding the protein confers on the cells a cold-sensitive phenotype (Schmid and Linder, 1992). Perhaps the apparent absence of cold-induced RNA chaperones in eukaryotic cells is... 

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

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