Chemistry of Life

Molecular genetics, biochemistry

helicases

Helicases are vital motor-protein enzymes that translocate in an enzyme specific direction (3'-5' or 5'-3') along a single-strand of a nucleic acid (DNA, RNA, DNA-RNA hybrids), often unwinding two strands of a double helix as they translocate. They employ energy generated by ATP hydrolysis and are employed in DNA replication, RNA transcription, DNA recombination, and DNA repair. []diagram of unwinding[] : 3'-5' DNA helicases :

helicases
"Since the discovery of the 'DNA unwinding enzyme,' it has become clear that helicases participate in virtually all cellular processes involving nucleic acids. Helicases are found in all three kingdoms of life and are extremely numerous: 1-2 percent of eukaryotic genes are helicases. Several severe human genetic diseases have been linked to mutations in helicases. . . The most fundamental activity for all helicases is translocation, the ability to move along nucleic acids. Translocation is powered by ATP hydrolysis; hence helicases are motor proteins. Many helicases function as a part of large macromolecular complexes. An example is chromatin remodeling, which regulates gene expression by controlling the DNA access in chromatin. Helicases are the central ATP-powered engines that drive the translocation of the chromatin-remodeling complexes along the DNA. . . Ha's lab measures FRET (fluorescence resonance energy transfer) between various sites on the protein and on the DNA to build dynamic structural models of the protein-DNA complex during translocation.

"HHMI News: DNA Enzyme Shows Unexpected Acrobatic Flair: "Helicase Protein: A helicase protein moving rapidly on a highly flexible single-stranded DNA track. Repetitive movement on the DNA may keep it clear of potentially toxic proteins. Watch Animation at Helicase 8KB Flash Animation(requires Flash Player) "

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. . . transcription begun 10/06/06