Tool enzymes

most of the restricted nucleic acid endoenzyme identification DNA sequence has echo structure characteristics, cut off the double-stranded DNA are produced 5' phosphate and 3' hydroxyl ends. Different restrictive nucleic acid intracutase identification and cutting specificity, the results are three different situations:

(1) produces 3' protruding sticky end (cohesive end): take Eoor as an example:

5'... G-AATT C... 3'→5'... Gp OHTTAAC... 3'

3'... C ATAA-G... 5'EooP I. 3'...CTTAAOH pG... 5'

(2) produces 5' prominent sticky ends: PstI. For example:

5'... CTGCA G... 3'→5'... CTGCAp OHG... 3'

3'... G-ACGTC... 5'PstI. 3'... GOH pACGTC... 5

(3) produces a flat end (blunt end): Nru I. For example:

5'... TCG CGA... 3'→5'... TCGp OHCGA... 3'

3'... AGC-GCT... 5'Nru I.3'... AGCOh pGCT... 5'

dna sequences identified by different restricted nucleic acid intra-cutting enzymes can be different. Some identify four nucleotide sequences, and some identify six or eight nucleotide sequences. If the nucleotide sequences in the DNA are randomly arranged, an internal cut enzyme that identifies the four nucleotide sequences occurs on average every 256bp at the identification cutting point of the enzyme, and the same pair of endoenzymes that identify the six or eight nucleotide sequences are roughly identified every 4kb or 65kb. Based on this, it can be roughly estimated that an unknown DNA molecular restrictive endoenzyme may have a cut-point frequency in order to select a suitable endoenzyme.

restricted nucleic acid intracutase variety, has been found nearly 800 kinds, according to their DNA has different identification sequences and cutting characteristics to choose from, thus providing a powerful tool forgene project. Table 20-2 lists the identification sequences and cutting points of some of the most commonly used restrictive nucleic acid endoenzymes.

G