Tus, also known as terminus utilization substance, is a protein that binds to terminator sequences and acts as a counter-
helicase
Helicases are a class of enzymes thought to be vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separatin ...
when it comes in contact with an advancing helicase.
The bound Tus protein effectively halts
DNA polymerase
A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...
movement.
Tus helps end
DNA replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
in
prokaryote
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conne ...
s.
[Slonczewski, Joan, and John Watkins. Foster. Microbiology: An Evolving Science. New York: W.W. Norton &, 2009. Print.]
In ''E. coli'', Tus binds to 10 closely related sites encoded in the
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
. Each site is 23 base pairs. The 10 sites are called
Ter site
In molecular biology, the ter site, also known as DNA replication terminus binding-site, refers to a protein domain which binds to the DNA replication terminus site. Ter-binding proteins are found in some bacterial species, and include the tus pro ...
s, and are designated ''TerA'', ''TerB'', ..., ''TerJ''. These binding sites are asymmetric, such that when a Tus-Ter complex (Tus protein bound to a Ter site) is encountered by a replication fork from one direction, the complex is dissociated and replication continues (permissive). But when encountered from the other direction, the Tus-Ter complex provides a much larger kinetic barrier and halts replication (non-permissive). The multiple ''Ter'' sites in the chromosome are oriented such that the two oppositely moving replication forks are both stalled in the desired termination region.
''
Bacillus subtilis
''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus ...
'' utilize replication terminator protein (RTP) instead of Tus.
Protein domains
The Ter protein contains two domains. The N-terminal domain is composed of an
alpha helices
The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...
, beta sheet, and three loops. The C-terminal domain is made of two
alpha helices
The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...
and one
beta sheet.
Further reading
* "Interaction of the Escherichia coli replication terminator protein (Tus) with DNA: a model derived from DNA-binding studies of mutant proteins by surface plasmon resonance."
* "Replication termination in Escherichia coli: structure and antihelicase activity of the Tus-Ter complex."
* "A molecular mousetrap determines polarity of termination of DNA replication in E. coli."
* "Isolation and characterization of mutants of Tus, the replication arrest protein of Escherichia coli."
* "Biophysical characteristics of Tus, the replication arrest protein of Escherichia coli."
* "Structure of a replication-terminator protein complexed with DNA."
*
Structure at protein data bank
References
DNA replication
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