Chromosome Jumping, Genomic DNA, Target Chromosome, Restriction Enzymes, DNA Fragments, tRNA Gene, Termination Codon,Library Hybridizes

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	Chromosome Jumping The technique of chromosome jumping is used for the creation of contigs and for construction of restriction maps of genomes. Chromosome jumping is used for rather large DNA fragments, usually of several hundred kb in size, while chromosome walking is applicable to much smaller DNA fragments. A simple approach to chromosome jumping uses 'jumping' and 'linking' libraries generated by a rare cutting enzyme, e.g., Not for humans.
Each clone in a jumping library contains the DNA sequences on one side each, e.g., sequences 2 and 3, of two neighbouring cutting sites of the enzyme NotI, while a clone in linking library has the DNA sequences located on either side of a single NotI, site, e.g., regions 1 and 2 in clone 1 and regions 3 and 4 in clone 2 to delete bulk of the DNA leaving only a small DNA sequence on either side of the SupF marker. The resulting fragments are ligated in a suitable λ vector and cloned. SupF is a tRNA gene that has a mutated anticodon, which recognizes a polypeptide chain termination codon generated by a suppressor-sensitive mutation within a gene.
Therefore, SupF serves as a selectable marker when it is introduced into an E. coli strain that carries the concerned suppressor-sensitive mutation within an essential gene, e.g., a gene involved in the biosynthesis of an essential metabolite. Similarly, the linking library clones are prepared. The genomic DNA is partially digested with a frequent cutting enzyme like Sau3A and the fragments are circularized in the presence 9f SupF. The circularized fragments are cut open with the enzyme NotI, and the liner fragments are integrated in a suitable A. vector. Only those circles that have a NotI site will become linear and, hence, integrate in the / vector.
Contig creation begins with the preparation of Y AC clones from the target chromosome, using, say NotI to digest the chromosomal DNA. The linking and jumping libraries are also made from DNA of the same chromosome using, say, NotI and BamHI restriction enzymes. Each clone of a linking library hybridizes with two different clones of the jumping library and vice versa. But each linking library clone will hybridize with only one Y AC clone, while each clone of jumping library will hybridize with two different Y AC clones; these relationships are illustrated. Each clone of the linking and jumping libraries is hybridized separately with all the Y AC clones obtained from the target chromosome.
	The data obtained from these hybridizations are pooled together to determine the correct order of various YAC clones leading to the creation of a contig for the chromosome in question. The procedure for construction of a NotI jumping library is, in simple terms, as follows. Genomic DNA is completely digested with NotI, and the resulting fragments are circularized in the presence of SupF marker. The circularised fragments are digested with a frequent cutting enzyme like BamHI " .