M-13

M-13

3.    M-13

1.    It is a filamentous phase and consist of single stranded circular DNA molecule. The genome of M-13 is smaller only 6407 nucleotide than $\lambda$ vector, this is because capsid protein of M-13 phage is encoded by multiple copies of three genes only, while capsid of $\lambda$ phage is synthesized from over 15 proteins which forms head and tail structure of $\lambda$ vector.
2.    Single strand DNA of M13 is called as + strand. In the E. coli cell, it is converted into double strand DNA called replication form (RF) by utilized E. coli machinery.
3.    This vector after replication release the host cell without cell lysis
4.    The life cycle of M13 virus is very much simpler than $\lambda$ vector and the entry of M13 virus in bacterial host occurs through F-pilus. This DNA molecule acts as a template for synthesis of a new strand of DNA. The complimentary strand of DNA is formed which results in the formation of double stranded DNA. But the DNA molecule do not integrate in bacterial host chromosome. This replicates till 100 copies are present in the host cell. If the host cell then each daughter cell receives the copies of M13 phage DNA molecules. These phage DNA molecules continue to divide to maintain the number of copies per cell. These phage particles are continuous assembled and are released from host cells without the lysis of the host cell since DNA molecules are released in single stranded form, therefore M13 phage molecules can be specifically used for amplifying those DNA molecules which are needed to be sequenced.
5.    The capsid of M13 phage puts constraint over the size of foreign DNA that can be ligated with phage molecule. The suitable size for proper packaging of DNA molecule in capsid is 38 to 51 kb in length. Therefore around 2.5 kb of exogenous DNA can be cloned by M13 phage. This limitation can be overcome by constructing vectors by using the essential genes of the host and accepting the foreign DNA to its theoretical maximum value.

$\rightarrow$    Use of M-13 vector
i.    DNA sequencing
ii.    Mutagenesis study
iii.    Probe generation
iv.    Probe display