The origins of replication

At the origin of replication (ori), there is an association of sequence-specific dsDNA-binding proteins with... 

ARS Autonomously replicating sequence the origin of replication in yeast. 

A hypercycle is a more complex organisation form. Its precondition is the presence of several RNA quasi-species which are able to amalgamate chemically with certain proteins (enzymes or their precursors). If such a protein is linked to a quasi-species, the resulting duo favours the replication of a second quasispecies. According to Dyson, the linked populations get stuck in a stable equilibrium. Problems occur at this level Any theory on the origin of replication has the central problem that the replication process must occur perfectly in order to ensure survival . If there are replication errors, these will increase from generation to generation, until the system collapses the error catastrophe has then occurred ... 

The base sequence at the origin of replication is recognized and bound by the dna A protein. The two parental strands of DNA are pulled apart to form a replication bubble. ... 

Figure 10. Cumulated skew profiles calculated around the origin of replication DNMTl Lamin B2, and P-globin in the human genome Sm (thick line) and Sec (thin line). The colors have the same meaning as in Fig. 9. See color insert.

In bacteria, replication starts at a specific point in the circular DNA—the origin of replication—and proceeds in both directions. This results in two diverging replication forks, in which the two strands are replicated simultaneously. Numerous proteins are involved in... 

B. Prokaryotic DNA replication is accomplished by DNA polymerases, large multienzyme complexes that move out bidirectionally from the origin of replication. 

DNA replication begins with protein binding to the origin of replication, a unique sequence in the bacterial chromosome, causing a short region of double-stranded DNA (dsDNA) to unwind (Figure 11-2). 

Burland, V. Plunkett, G. Daniels, D.L. Blattner, F.R. DNA sequence and analysis of 136 kilobases of the Escherichia coli genome organizational symmetry around the origin of replication. Genomics, 16, 551-561 (1993)... 

DNA replication begins at the origin of replication (one in prokaryotes, multiple in eukary otes). The strands are separated locally, forming two replication forks. Replication of double-stranded DNA is bidirectional. 

A group of proteins form the prepriming complex. They recognize the origin of replication (dnaA protein), maintain the separation of the parental strands (single-stranded DNA-binding proteins), and unwind the double helix ahead of the advancing replication fork (helicase). 

The use of autoradiographic methods confirmed bidirectional replication. Strains of amino acid aux-otrophs with small nucleoside triphosphate pools were used. The addition of amino acids after starvation led to initiation of replication with only a 6-min lag. The cells were labeled with [3H]thymidine, and after the replication forks had moved a short distance from the origin of replication the cells were given a pulse of "super-hot" [3H]thymidine. Using autoradiography it was possible to observe the clearly bidirectional replication forks378 (Fig. 27-17). Replication in other bacteria is also bidirectional. 

It has long been postulated that the bacterial chromosome is attached to the plasma membrane. At least one such attachment site may be at or near the origin of replication.393 Furthermore, the exchange of ADP for ATP in the dnaA protein is catalyzed specifically by cardiolipin and phosphati-dylglycerol containing the unsaturated oleic acid.386 393 Inositol polyphosphates may also play a role 394... 

Initiation of replication in metazoans is still confusing. Almost any piece of DNA will be replicated if introduced into a Xenopus egg, where initiation appears to occur just once at a random position.501 501a b However, in differentiated tissue the origins of replication seem to be fewer in number and more specifically located. A possible explanation is that high concentrations of ORC and MCM proteins in the embryo may lead to many relatively nonspecific origins and a replicon size of 7 kb. The lower concentrations of these auxiliary factors in somatic cells may lead to fewer but more specific origins with a replicon size... 

Antisense RNA. Another mechanism of control of either transcription or of plasmid replication involves small molecules of RNA that are transcribed from the opposite strand than the template strand used for mRNA synthesis.1 13 165-166b These antisense RNA molecules have at least some part of their sequence complementary to that of the mRNA and to the corresponding sequence in DNA. A well-studied example is control of the copy number of the colicin El and other plasmids of E. co/i.167-169 Two transcripts, RNAI and RNAII, are initiated upstream from the origin of replication (Fig. 28-8). RNA II is a 555-nucleotide primer of replication. It is synthesized as a longer transcript that is cut by RNase H at ori. This... 

The development of an efficient cell-free replication system has greatly accelerated progress in understanding the molecular mechanisms involved in SV40 DNA replication. The origin of replication is recognized by the viral T anti-... 

Replication starts by the separation of the strands of DNA and the formation of a local bubble at a specific DNA site called the origin of replication (ori). A helicase enzyme uses energy from ATP hydrolysis to effect this action. Single-strand DNA binding proteins stabilize the strands during the subsequent steps. The original DNA strands will function as the templates that will direct synthesis of the complementary strands. A nucleotide on the template strand will determine which deoxyribonucleotide (dNTP) will be incorporated in the newly synthesized strand. This replica-... 

Chain initiation occurs when a specialized RNA polymerase enzyme called primase makes a short RNA primer. DNA polymerase III extends this RNA primer on both strands. Because DNA polymerase synthesizes DNA only in one direction (5 to 3 ), only one strand is copied in each direction (left and rightward in the next figure). At the end of the initiation process, two replication forks exist, going in opposite directions from the bubble at the origin of replication, as shown in Figure 8-11. 

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