An autonomously replicating sequence (ARS) contains the

origin of replication The origin of replication (also called the replication origin) is a particular sequence in a genome at which replication is initiated. Propagation of the genetic material between generations requires timely and accurate duplication of DNA by semi ...

in the

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

. It contains four regions (A, B1, B2, and B3), named in order of their effect on

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

stability. The A-Domain is highly conserved, any mutation abolishes origin function. Mutations on B1, B2, and B3 will diminish, but not prevent functioning of the origin. Element A is highly conserved, consisting of the consensus sequence: (where ''Y'' is either

pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The other ...

and ''R'' is either

purine Purine is a heterocyclic compound, heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which includ ...

). When this element is mutated, the ARS loses all activity. As seen above the ARS are considerably A-T rich which makes it easy for replicative proteins to disrupt the H-bonding in that area. ORC protein complex (

origin recognition complex In molecular biology, origin recognition complex (ORC) is a multi-subunit DNA binding complex (6 subunits) that binds in all eukaryotes and archaea in an ATP-dependent manner to origins of replication. The subunits of this complex are encoded ...

) is bound at the ARS throughout the

cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and subs ...

, allowing replicative proteins access to the ARS. Mutational analysis for the yeast ARS elements have shown that any mutation in the B1, B2 and B3 regions result in a reduction of function of the ARS element. A mutation in the A region results in a complete loss of function. Melting of DNA occurs within domain B2, induced by attachment of ARS binding factor 1 to B3. A1 and B1 domain binds with origin recognition complex. To identify these sequences, yeast mutants unable to synthesize

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...

were transformed with plasmids containing the His gene and random fragments of the yeast genome. If the genome fragment contained an origin of replication, cells were able to grow in a medium lacking histidine. These sequences were termed autonomously replicating sequences, because they were replicated and inherited by progeny without integrating into the host

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 ...

References

{{DEFAULTSORT:Autonomously Replicating Sequence Genomics techniques