Bacteria endonuclease

Phospholipase D is widely distributed in bacteria, fungi, plants and animals, and is present in almost all mammalian cells [3]. In mammals, it occurs as alternatively spliced products of two genes (PLD1 andPLD2) (Fig. 3). Most mammalian cells express different levels of both isoforms. Both PLD1 and PLD2 have four conserved sequences (I-IV), and sequences I and IV contain the HXKX4D (HKD) motif that is characteristic of the PLD superfamily, which includes bacterial endonucleases, phospholipid synthases, viral envelope... 

Restriction Endonuclease Bacteria Sequence Recognized" Ends"... 

These enzymes are isolated from bacteria, their natural source. There are many different restriction endonucleases isolated from a variety of bacteria that are now readily available commercially. In bacteria they act as part of a restriction/modification system that protects the bacteria from infection by DNA viruses. 

Bacteria contain enzymes that catalyse the breaking of phosphodiester links between nucleotides in DNA at specific sites, to which the enzyme is directed by a short sequence of bases. These are known as restriction enzymes and they have resulted in remarkable progress in analysing sequences of DNA fragments. They are endonucleases, i.e., they cleave DNA at the phosphodiester bonds within, rather than at the ends, of DNA chains. They cleave bonds such that sequences of nucleotides, typically 4-8 base pairs, are produced. These are the restriction sequences. 

To isolate a gene, scientists use surgical DNA scissors called restriction endonucleases (RE), proteins made by bacteria that cut DNA, based on specific rules. Each kind of RE—there are hundreds— recognizes specific sequences of 4-8 base pairs and cuts the DNA molecule at a specific spot (Figure 1.2). The biotechnologist selects... 

DNA suitable for the insertion of foreign DNA is known as a vector the most commonly used vectors in bacteria are plasmids. Plasmids are small (2-3 kb) loops of DNA found in bacteria and yeast. They were first discovered when it was observed that bacteria could pass antibiotic resistance from one colony to another. This process was demonstrated to be mediated by plasmids containing genes for enzymes that inactivated the antibiotics. In addition to the work on plasmids, other research laboratories have isolated enzymes that cut DNA at specific sequences (restriction endonucleases) and other enzymes that can rejoin these cuts again (DNA ligases). 

Type II restriction endonucleases recognize specific base sequences in double-stranded DNA, and cleave both strands of the duplex. More than 600 restriction endonucleases have been reported in the literature. Some 121 restriction endonucleases are listed in Current Protocols in Molecular Biology as commercially available ( 3). Table II, adapted from the 1988 Sigma Chemical Company Catalog, lists 35 of the endonucleases available from that source. Endonucleases are found in many bacteria where their function is to hydrolyze foreign DNA introduced by phage infection, conjugation or transformation. The first restriction endonucleases were discovered and isolated in 1968 (4,5). 

Adopting a new gene. Suppose that one species of bacteria obtained one gene encoding a restriction endonuclease by horizontal gene transfer. Would you expect this acquisition to be beneficial ... 

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