Difference Between YAC and BAC Vectors

The main difference between YAC and BAC vectors is that the YAC vectors (Yeast Artificial Chromosome vectors) contain the molecular components for the replication inside yeast whereas the BAC vectors (Bacterial Artificial Chromosome Vectors) contain molecular components for the replication inside bacteria. Furthermore, the size of the insert carried by YAC vectors is 100-1000 kb while the size of the insert carried by BAC vectors is 100-200 kb. 

YAC and BAC vectors are two types of artificial vector systems designed to clone large genomic DNA fragments. They have multiple applications in the preparation of genomic and cDNA libraries.  

Key Areas Covered 

1. What are YAC Vectors
     – Definition, Features, Construction
2. What are BAC Vectors
     – Definition, Features, Applications
3. What are the Similarities Between YAC and BAC Vectors
     – Outline of Common Features
4. What is the Difference Between YAC and BAC Vectors
     – Comparison of Key Differences

Key Terms 

BAC Vectors, Cloning Capacity, Host, Vector Components, YAC Vectors 

What are YAC Vectors 

YAC (Yeast Artificial Chromosome) vectors are a type of artificial chromosomes designed to transform into yeast cells after cloning large DNA fragments. It consists of the elements of a typical yeast chromosome. They are; 

1. CEN – A yeast centromere, which ensures the segregation into two daughter cells during reproduction. 
2. ARS – Origin of replication for the autonomous replication inside the yeast cell 
3. TEL -Telomeric region 
4. TRP1 and URA3 – Selectable marker genes for the selection of transformed yeast cells 
5. Bacterial selectable marker gene 
6. BamHI and EcoRI restriction sites – For the linearization and insertion of the DNA fragment 

Construction of YAC Vectors 

1. Linearization of a circular, DNA plasmid by restriction digestion with BamHI 
2. Restriction digestion with EcoRI  
3. Ligation with the DNA fragment of interest 
   

   Figure 1: Construction of YAC Vector

Some  examples of YAC vectors are YAC72 and YAC46. The size of the DNA fragment that can be inserted into a YAC vector is 100-1000 kb. 

What are BAC Vectors 

BAC (Bacterial Artificial Chromosome) vectors are a type of artificial chromosomes designed to transform into bacteria, especially E. coli, after cloning large DNA fragments. The size of the DNA fragment that can be inserted into a BAC vector is 100-200 kb. The structure of the BAC vector is based on the fertility plasmid/F-plasmid. The common components of a BAC vector are; 

1. repE – Mediates the assembly of the replication complex 
2. parA and parB – For the partitioning of genes during replication 
3. Selectable marker – For the selection of transformants; can be an antibiotic resistance gene or LacZ 
4. T7 and SP6 – Promote the transcription of the insert 
5. OriS – For the unidirectional origin of replication 
   

   Figure 2: Construction of BAC Vector

BAC vectors were often used in sequencing during the Human Genome Project. BAC vectors are used in the modeling of genetic diseases such as Down syndrome and neurological diseases such as Alzheimer’s disease. Also, the genomes of some large, DNA and RNA viruses are cloned into BAC vectors. PAC is a similar vector to BAC, which is produced based on the P1 bacteriophage. 

Similarities Between YAC and BAC Vectors 

• YAC and BAC vectors are artificial vector systems designed for the insertion of large DNA fragments. 
• Both come as circular plasmids. 
• They have multiple applications in the preparation of genomic and cDNA libraries.  

Difference Between YAC and BAC Vectors 

Definition 

The YAC vectors refer to a vector (carrier) constructed from the telomeric, centromeric, and replication origin sequences needed for replication in yeast cells while the BAC vectors refer to a DNA construct based on a functional fertility plasmid (or F-plasmid), used for transforming and cloning in bacteria, usually E. coli.  

Host 

YAC vectors are transformed into yeast cells while BAC vectors are transformed into bacteria. 

Based on 

The YAC vector is produced based on the specific regions of the yeast chromosome while the BAC vectors are produced based on the F-plasmid.  

Configuration 

YAC vectors are linear while BAC vectors are circular. 

Copy Number 

A single YAC vector occurs per yeast cell while 1-2 BAC vectors occur per bacterial cell. 

Cloning Capacity 

YAC vectors have a high cloning capacity as its insert can be up to 1000 kb in size while BAC vectors have less cloning capacity as its insert can be up to 200 kb in size. 

Conclusion 

The YAC vector is an artificial vector system with a high cloning capacity (up to 1000 kb) while BAC vector is an artificial vector system with a low cloning capacity (up to 200 kb) when compared to YAC. YAC vectors are transformed into yeast cells while BAC vectors are transformed into bacteria. The main difference between YAC and BAC vectors is their cloning capacity and host.

Reference:

1. Monaco, Anthony P, and Zoia Larin. “YACs, BACs, PACs and MACs: Artificial Chromosomes as Research Tools.” Trends in Biotechnology, Elsevier, 26 Aug. 2004, Available Here

Image Courtesy:

1. “Construction of a YAC chem114A” By Tinastella at English Wikibooks – Transferred from en.wikibooks to Commons. (Public Domain) Available Here
2. “BACs cloning vectors Chem114A” By Tinastella (CC BY-SA 3.0) via Commons Wikimedia