Wikipedia
HindIII (pronounced "Hin D Three") is a type II site-specific deoxyribonuclease restriction enzyme isolated from Haemophilus influenzae that cleaves the DNA palindromic sequence AAGCTT in the presence of the cofactor Mg via hydrolysis. The cleavage of this sequence between the AA's results in 5' overhangs on the DNA called sticky ends:
5'-A |A G C T T-3'
3'-T T C G A| A-5'
Restriction endonucleases are used as defense mechanisms in prokaryotic organisms in the restriction modification system. Their primary function is to protect the host genome against invasion by foreign DNA, primarily bacteriophage DNA. There is also evidence that suggests the restriction enzymes may act alongside modification enzymes as selfish elements, or may be involved in genetic recombination and transposition.