Yeast artificial chromosome - AbsoluteAstronomy.com

A yeast artificial chromosome (YAC) is a vector

Vector (molecular biology)

In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...

used to clone

Molecular cloning

Molecular cloning refers to a set of experimental methods in molecular biology that are used to assemble recombinant DNA molecules and to direct their replication within host organisms...

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

fragments larger than 100 kb

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

and up to 3000 kb. YACs are useful for the physical mapping of complex genomes and for the cloning of large genes. First described in 1983 by Murray and Szostak

Jack W. Szostak

Jack William Szostak is a Canadian American biologist of Polish British descent and Professor of Genetics at Harvard Medical School and Alexander Rich Distinguished Investigator at Massachusetts General Hospital, Boston. He was awarded the 2009 Nobel Prize for Physiology or Medicine, along with...

, a YAC is an artificially constructed chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

and contains the telomeric

Telomere

A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...

, centromeric

Centromere

A centromere is a region of DNA typically found near the middle of a chromosome where two identical sister chromatids come closest in contact. It is involved in cell division as the point of mitotic spindle attachment...

, and replication origin

Origin of replication

The origin of replication is a particular sequence in a genome at which replication is initiated. This can either be DNA replication in living organisms such as prokaryotes and eukaryotes, or RNA replication in RNA viruses, such as double-stranded RNA viruses...

sequences named autonomous replicating sequence needed for replication and preservation in yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

cells. A YAC is built using an initial circular plasmid

Plasmid

In microbiology and genetics, a plasmid is a DNA molecule that is separate from, and can replicate independently of, the chromosomal DNA. They are double-stranded and, in many cases, circular...

, which is typically broken into two linear molecules using restriction enzyme

Restriction enzyme

A Restriction Enzyme is an enzyme that cuts double-stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...

s; DNA ligase

DNA ligase

In molecular biology, DNA ligase is a specific type of enzyme, a ligase, that repairs single-stranded discontinuities in double stranded DNA molecules, in simple words strands that have double-strand break . Purified DNA ligase is used in gene cloning to join DNA molecules together...

is then used to ligate a sequence or gene of interest between the two linear molecules, forming a single large linear piece of DNA.

Yeast expression vectors, such as YACs, YIps

Yips

Yips or the yips is an expression used to describe the apparent loss of certain fine motor skills seemingly without explanation in one of a number of different sports....

(yeast integrating plasmids), and YEps (yeast episomal plasmids), have an advantage over bacterial artificial chromosome

Bacterial artificial chromosome

A bacterial artificial chromosome is a DNA construct, based on a functional fertility plasmid , used for transforming and cloning in bacteria, usually E. coli. F-plasmids play a crucial role because they contain partition genes that promote the even distribution of plasmids after bacterial cell...

s (BACs) in that they can be used to express eukaryotic proteins that require posttranslational modification

Posttranslational modification

Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis, and thus gene expression, for many proteins....

. However, YACs have been found to be less stable than BACs, producing chimeric effects.

A typical YAC consists of centromere element (CEN) for chromosome segregation during cell division, telomere and origin of replication (ori) were isolated and joined on plasmid constructed in E.coli. For cloning purpose YAC is digested with restriction enzymes and recombinants are produced by inserting a large fragment of genomic DNA. This molecule can be maintained in yeast as YAC. The transformant that contain YAC can be identified by red/white color selection. Non-transformed yeast contain white colonies. Red colonies of yeast contain recombinant YAC molecule. Due to insertion of DNA molecule into EcoR1 site, SUP4 gene is inactivated and no proteins will be expressed . This facilitates to develop red colonies.

See also