The restriction enzymes cut the DNA at a specific point called recognition sequence or sites. Each restriction enzyme has it particular restriction site. Without the recognition sequences the restriction endonuclease would cleave the DNA anywhere and it would be very difficult to know the length of the fragments generated on cleavage and which target sites to use in making molecular probes.
Thus, the recognition sequences play a vital role in giving direction to the restriction enzymes regarding the particular position of cleavage in the DNA.
For example:
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The recognition sequence for EcoRI enzyme is
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5' GAATTC 3'
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3' CTTAAG 5'
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While that for HindIII enzyme is
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5' AAGCTT 3'
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3' TTCGAA5'
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Each enzyme having its own recognition sequence
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