Difference between YAC and BAC Vectors

A vector is a stretch of DNA that acts as a transport for carrying foreign genetic material into host cells, where it can replicate and express itself. The four types of vectors are plasmids, viral vectors, cosmids and artificial chromosomes.

Vectors are constructed for different purposes. The vectors that are used for the expression of the target gene are called expression vectors, vectors that are used for transcription are called transcription vectors (they cannot translate), and vectors that are able to express in more than one host are called shuttle vectors.

The insertion of vectors into bacteria is called transformation, into eukaryotic cells is called transfection and insertion of viral vectors is called transduction.

Vectors that are able to carry larger gene sequences than any other vector are referred to as artificial chromosomes.. Bacterial artificial chromosomes (BACs), Human artificial chromosomes (HACs), and Yeast artificial chromosomes (YACs) are some examples of artificial chromosomes.

What are YAC Vectors?

Yeast Artificial Chromosomes (YACs) are artificially constructed vectors. The system can undergo replication and has the capability to insert foreign DNA sequences.

Components such as the autonomously replication system (ARS), centromere and telomeres are taken from the yeast Saccharomyces cerevisiae for the construction of vectors.

The desired gene sequence can be inserted into these vectors and then put back into yeast; the yeast machinery cannot differentiate between their own and foreign genes; hence the foreign gene is also replicated.

Refer: Plasmid

What are BAC Vectors?

Bacterial Artificial Chromosomes (BACs) are DNA constructs that are used for transformation and cloning in bacterial cells, mostly E.coli. Functional fertility plasmids or F-plasmids are used for the vector construction.

The gene components included are rep6 for plasmid regulation, a selectable marker for antibiotic resistance, parA and parB for F-plasmid DNA, and T7 and Sp6 for transcription of inserted genes.

Let us now see the differences between a YAC and a BAC vector.

YAC Vector

BAC Vector

Description

YAC vectors are DNA constructs that are used for cloning DNA in yeasts.

BAC vectors are DNA constructs that are used for cloning DNA in bacteria.

Gene insert

A gene sequence of 100-1000 kbp can be inserted in these vectors.

A gene sequence of 150-350 kbp can be inserted into the BAC vectors.

Chimerism

They often show chimerism.

No chimerism seen.

Shape of the construct

It is linear.

It is circular.

PTM

Yeast machinery has post-translational mechanisms that are useful in the expression of eukaryotic proteins.

Bacterial machinery does not have PTM mechanism, hence the expression of eukaryotic proteins becomes difficult.

Number of vectors

Only one vector occurs per yeast cell.

1-2 vectors are found per bacterial cell.

Stability

Less stable.

More stable.

Disadvantages

There are chances of gene deletion and gene recombination or inversion in the inserted gene sequence.

BACs do not have such disadvantages.

Advantages

YACs do not have such advantages.

The generation of BACs is quicker and more efficient, and also, it gives a better chromosome coverage map.

Application

  • Gene Mapping
  • Chromosome Walking
  • Modelling Genetic Diseases
  • Human Genome Project

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Frequently Asked Questions

Which is better, YAC or BAC?

Today, BAC is preferred over YAC because they are more efficient.

Why are shuttle vectors called so?

Shuttle vectors are called because genes inserted into these vectors can be tested and expressed in two different hosts.

What is MCS in cloning?

MCS stands for Multiple Cloning Sites in a vector where multiple restriction sites are present.

Is BAC a shuttle vector?

The pGNS-BAC-1 plasmid is a shuttle vector.

What are the characteristics of a shuttle vector?

Shuttle vectors have higher transformation efficiency, higher plasmid copy number, and the stability of plasmids is also seen.

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