Introduction
Genetic manipulation has proven to be a relatively straightforward process in prokaryotes and lower eukaryotes. However, when it comes to higher eukaryotes, multicellular plants, and animals, it becomes a significantly more challenging task. The primary objective of genetic engineering is to express genes in plant and animal cells through tissue culture and study their expression or production of useful proteins. Additionally, it involves the development of transgenic organisms by altering the genetic makeup of these organisms. It is crucial to introduce genetic changes or new genes during the early stages of development to ensure the spread of recombinant sequences throughout the organism.
To carry out genetic modifications and sequencing of genomes, scientists rely on vectors. Vectors are vehicles that transport foreign DNA into host cells. However, for sequencing purposes, vectors with a larger carrying capacity are required. This led to the development of vectors specifically designed for sequencing, such as the Bacterial Artificial Chromosome (BAC), which played a significant role in the Human Genome Project.
Bacterial Artificial Chromosomes (BACs)
- BACs are based on the F plasmid and enable the integration of large DNA inserts, ranging from a few hundred kilobases into the host genome.
- These vectors were utilized during the human gene sequencing project due to their ability to carry up to 300 kb long DNA fragments.
- BACs have several important features and components:
- Cloning of large DNA fragments (100 – 300 kb) in E. coli.
- BACs contain the origin of replication (ori) of the F-plasmid, which controls replication and maintains a low copy number.
- Transfer occurs through conjugation between F+ and F- cells.
- Key elements of BACs include RepE, which regulates copy number, Par A and Par B for partition during cell division, selectable markers, and T7 and Sp6 phage promoters for transcription.
- Examples of BAC vectors include pBAC 108L, pBeloBAC11, and pECBAC1.
P1 Derived Artificial Chromosomes (PACs)
- Developed by Sternberg and co-workers in 1990, P1 Derived Artificial Chromosomes (PACs) are based on the P1 bacteriophage.
- The P1 phage is known for its ability to mediate the generalized transduction process in E. coli. PAC vectors can carry DNA fragments of approximately 100-200 kb in size.
- Some key features of PACs are:
- PACs contain a kanamycin-resistant marker and can achieve a high copy number using the P1 lytic replicon.
- They are commonly used in genome sequencing and genetic libraries of various organisms, including mice, humans, and drosophila.
- An example of a PAC vector is pESAC13.
Yeast Artificial Chromosomes (YACs)
- Yeast Artificial Chromosomes (YACs) are engineered DNA molecules used to clone DNA sequences in yeast cells.
- They were first developed by Murray and Szostak in 1983.
- YAC vectors can carry DNA fragments ranging from 1-2 Mb in size. Key components of YACs include:
- Yeast origin of replication (ARS)
- Selection markers for both the host organism and yeast
- Centromere and telomere regions from yeast chromosomes
- YAC vectors, denoted as pYAC, serve as shuttle vectors due to the presence of both E. coli ori and yeast ARS.
Mammalian Artificial Chromosomes (MACs)
- Mammalian Artificial Chromosomes (MACs) share similarities with YACs as they also possess centromeric and telomeric regions, along with origins of replication.
- They undergo autonomous replication and segregation in mammalian cells.
- Two main methods for generating MACs include telomere-directed fragmentation of natural chromosomes and de novo assembly of cloned centromeric and replication origins in vitro.
- Mammalian DNA’s higher degree of repetition and larger centromere and telomere regions contribute to the generation of MACs.
Conclusion
In conclusion, Artificial Chromosomes have opened up new avenues in genetic engineering and recombinant DNA technology. Their ability to mimic natural chromosomes allows scientists to manipulate and study genes more effectively. Bacterial artificial chromosomes (BACs), P1 derived artificial chromosomes (PACs), yeast artificial chromosomes (YACs), and mammalian artificial chromosomes (MACs) are prominent examples of these engineered structures. Each type serves specific purposes and has revolutionized genomic research. By harnessing the power of Artificial Chromosomes, scientists can further unravel the complexities of genetic information.
Frequently Asked Questions (FAQs)
Q. What is the purpose of Artificial Chromosomes in genetic engineering?
A. Artificial Chromosomes serve as engineered structures that mimic natural chromosomes, enabling scientists to manipulate and study genes more effectively in higher eukaryotes and multicellular organisms.
Q. What is the significance of Bacterial Artificial Chromosomes (BACs)?
A. BACs played a vital role in the Human Genome Project as they have a larger carrying capacity and can integrate DNA fragments up to 300 kb long. They are used for cloning and sequencing purposes.
Q. How are P1 Derived Artificial Chromosomes (PACs) different from BACs?
A. PACs are based on the P1 bacteriophage and can carry DNA fragments of approximately 100-200 kb in size. They are commonly used in genome sequencing and genetic libraries.
Q. What are the applications of Yeast Artificial Chromosomes (YACs)?
A. YACs are used to clone DNA sequences in yeast cells and carry larger DNA fragments, ranging from 1-2 Mb. They serve as valuable tools in genomic research and allow for the study of gene expression and regulation.
Q. How are Mammalian Artificial Chromosomes (MACs) generated?
A. MACs can be generated through telomere-directed fragmentation of natural chromosomes or by assembling cloned centromeric and replication origins in vitro. They undergo autonomous replication and segregation in mammalian cells.
