tailieunhanh - analysis of genes and genomes phần 4

có liên quan với tái tổ hợp và các quá trình của lysogeny trong đó các nhiễm sắc thể circularized thể thực khuẩn được đưa vào nhiễm sắc thể chủ và ổn định được nhân rộng như một prophage. | 128 VECTORS 3 l infection l DNA inserted into E. coli l DNA circularises via cos sites Lysogenic pathway Lytic pathway l DNA integrated into E. coll genome l DNA replicated Rolling circle replication l prophage replicated with E. coll genome DNA cleaved at cos sites and packaged into newly synthesised head particles Cell lysis and phage release X VECTORS 129 are concerned with recombination and the processes of lysogeny in which the circularized phage chromosome is inserted into the host chromosome and is stably replicated as a prophage. To the right of the map are genes concerned with transcriptional regulation and prophage immunity to superinfection N cro cI followed by the genes for DNA synthesis late function regulation Q and host cell lysis. Our extensive knowledge of X phage and the ways in which the lytic and lysogenic life cycles are regulated have made X an ideal vector to carry foreign DNA fragments. The major advantage of X based vectors over plasmids is the efficiency at which the phage can infect E. coli cells. As we have already discussed the transformation of plasmid DNA into bacteria is not an efficient process whereas X infection is a very efficient way to introduce DNA into a bacterial cell. To understand how X can be exploited as a vector it is important to have a basic knowledge of the phage itself. X phage infection and lysis occurs in number of defined steps. Infection occurs as a result of the adsorption of the X phage particle to the bacterial cell by binding to the maltose receptor. The X genomic DNA is injected into the cell and almost immediately circularizes. At this point it can enter one of two pathways. Lysogenic pathway. The phage DNA becomes integrated into the bacterial genome via homologous recombination between attP and the bacterial genomic attB site and is replicated along with the bacterial DNA. The prophage DNA remains integrated until it is induced to enter the lytic pathway. Lytic pathway. Large-scale production of .