Biology of microbes
Philip A. Geis in Cosmetic Microbiology, 2006
To understand the process in detail requires far more effort. In reality, at least seven enzymes are involved in the process described in the paragraph above: initiator protein, helicase, polymerases, repair nucleases, topoisomerase, single-strand DNA-binding proteins, and DNA ligase. The initiator protein first finds the right place to begin copying and guides the helicase to the correct position (an origin of replication site) on the nucleic acid. The helicase separates the DNA by breaking the weak bonds between the nucleotides to unwind the two strands of DNA. Then the polymerases arrive to join the free nucleotides to their matching complements on the old strands using the phosphate bond energy from the nucleotide to help form the new bond to the other nucleotides as they are added to the existing chain. These polymerases work along with primases that first synthesize a short (one to five nucleotides long) RNA primer. This primer allows DNA polymerase to begin catalyzing the addition of nucleotides to a new strand complementary to the existing template upon which the new DNA synthesis is based.
The Premature Aging Characteristics of RecQ Helicases
Shamim I. Ahmad in Aging: Exploring a Complex Phenomenon, 2017
The DNA-binding activities of RecQ4 have been further characterized in recent studies, revealing that the N-terminus of human RecQ4 contains regions of intrinsic disorder, but this disorder is sufficient for strand annealing activity [148]. Multiple DNA-binding sites are observed to be present, and this N-terminal region has the highest affinity of G4 quadruplex DNA, estimated at 60-fold over other substrates that include single-stranded, double-stranded, and Y-structured DNA [148]. G4 quadruplex elements are present near origins of replication, likely highlighting RecQ4 functions in this process. A separate study also indicated the presence of two key sites in the N-terminus for DNA binding, and the helicase core contained a third that has affinity for branched substrates and in particular, Holliday junctions [149].
Role of telomeres and telomerase in aging and cancer
J. K. Cowell in Molecular Genetics of Cancer, 2003
The gene responsible for WS (WRN) has been cloned and encodes a protein with homology to the E. coli RecQ (Yu et al., 1996). The RecQ protein binds single-stranded DNA and has a 3’→5’ helicase activity (Umezu et al., 1990). That helicase function is dependent on ATP hydrolysis and is stimulated (> 100 fold) by single strand binding protein (Umezu and Nakayama, 1993). RecQ can resolve a wide variety of substrates including recombinational joint molecules generated by RecA protein (Harmon and Kowalczykowski, 1998). These properties of RecQ led to the suggestion that it may improve the fidelity of recombination by dissociating illegitimate recombination events that are initiated through microhomology. Reintroduction of the WRN gene into WS cells complements the premature senescence phenotype of WS cells (Hisama et al., 2000). Similarly, introduction of an exogenous hTERT gene into WS cells yields suppression of senescence of WS cells, as it does for most other cell types tested (Ouellette et al., 2000; Wyllie et al., 2000). Another report indicates that the introduction of hTERT gene into WS cells can render partial correction of the 4NQO sensitivity of those cells (Hisama et al., 2000). This suggests that the 4NQO sensitivity is intimately linked to telomere length.
Emergence of varicella-zoster virus resistance to acyclovir: epidemiology, prevention, and treatment
Published in Expert Review of Anti-infective Therapy, 2021
Kimiyasu Shiraki, Masaya Takemoto, Tohru Daikoku
Double-stranded DNA needs to be separated into two single strands (replication fork) before DNA synthesis, and complementary strands are synthesized from each DNA strand to produce two new double-stranded DNA molecules during DNA replication (Figure 3). The HP complex is responsible for unwinding viral DNA at the replication fork, separating double-stranded DNA into two single strands, and synthesizing RNA primers (Okazaki fragments) in the lagging strand for DNA synthesis. DNApol initiates complementary DNA synthesis in the two separated DNA strands. The HP complex consists of three proteins: VZVORF55 (helicase), VZVORF6 (primase), and VZVORF52 (cofactor). The helicase unwinds the duplex DNA ahead of the fork and separates the double strand into two single strands. The primase lays down RNA primers that extend the two-subunit DNApol. The HP complex possesses multienzymatic activities, including DNA-dependent ATPase, helicase, and primase activities, all of which are required for the HP complex to function in viral DNA replication.
Enhancing radiosensitisation of BRCA2-proficient and BRCA2-deficient cell lines with hyperthermia and PARP1-i
Published in International Journal of Hyperthermia, 2018
Arlene L. Oei, Vidhula R. Ahire, C. M. van Leeuwen, Rosemarie ten Cate, Lukas J. A. Stalpers, Johannes Crezee, H. Petra Kok, Nicolaas A. P. Franken
DNA is replicated during the S-phase of the cell cycle. Enzyme helicase unzips DNA strands, creating a replication fork, where multiple proteins can bind. These proteins can restore DNA damage thereby preventing genome instability, before DNA replication may proceed [1]. If DNA replication is compromised, DNA damages, such as single strand breaks (SSBs) may occur. One of the proteins that is recruited at sites of stalled forks is Poly(ADP-ribose)polymerase1 (PARP1). Along with other repair proteins, PARP1 binds to the DNA and repairs damages and reinitiates DNA replication at the stalled forks [2]. If PARP1 cannot cope with these SSBs during this semi-conservative repair process, the SSBs can be converted to DNA double strand breaks (DSBs) or also referred to as a double strand end (DSE) [3]. Consequently, this primarily activates homologous recombination (HR) to repair DNA damage in the S- and G2-phases of the cell cycle [4,5]. Thus, as PARP1 is required for regulating replication integrity, interference by PARP1-inhibitors (PARP1-i) gives rise to DSEs caused by failures during DNA replication.
Development and implementation of precision therapies targeting base-excision DNA repair in BRCA1-associated tumors
Published in Expert Review of Precision Medicine and Drug Development, 2019
Adel Alblihy, Katia A. Mesquita, Maaz T. Sadiq, Srinivasan Madhusudan
RecQ helicase proteins are a highly conserved family of proteins with a vital role in genomic stability. They include WRN, RECQL5 and BLM helicases. Changes in the expression of these genes are correlated with breast cancer, suggesting that they may be biomarkers for breast cancer [136]. High BLM mRNA and protein levels have been linked to poor breast cancer-specific survival [137]. In addition, topoisomerase 1 and WRN expression have been associated with an aggressive form of breast cancer and poor prognosis. High level of RECQL5 mRNA has been found in 34% of the breast cancers and is significantly correlated with an aggressive phonotype. Similarly, high RECQL5 protein level has been found in more than half of breast cancers and is associated with the aggressive phenotype and poor survival, although only in correlation with low RAD51 levels, highlighting the possible interaction between these two proteins. It also revealed that RECQL5 expression in noncancerous breast epithelial cells plays a role in increasing proliferation, proposing an oncogenic role in breast cancer [137]. RECQL5 is a target for monotherapy and combined therapy for cancer treatment. WRN and BLM induce synthetic lethality with other DNA damage response proteins. Moreover, the depletion of WRN and BLM have shown to increase the sensitization of cancer cells to chemotherapeutic agents [138,139].
Related Knowledge Centers
- Directionality
- DNA
- Enzyme
- Genome
- Hydrolysis
- Motor Protein
- Nucleic Acid
- Phosphodiester Bond
- Nucleic Acid Double Helix
- Adenosine Triphosphate