Cloning, nucleotide sequence, and expression of theHincll restriction-modification system

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Abstract
Two genes, coding for the Hincll from Haemophilus influenzae Re restriction-modification system, were cloned and expressed in Escherichia coli RR1. Their DNA sequences were determined. The Hincll methylase (M.Hincll) gene was 1, 506 base pairs (bp) long, corresponding to a protein of 502 amino acid residues (Mr=55, 330). The Hincll endonuclease (R.Hincll) gene was 774 bp long, corresponding to a protein of 258 amino acid residues (Mr = 28, 490). The amino acid residues predicted from the R.Hincll and the N-terminal amino acid sequence of the enzyme found by analysis were identical. These methylase and endonuclease genes overlapped by 1 bp on the H. infiuenzae Re chromosomal DNA. The clone, named E. coli RR1-Hincll, overproduced R.Hincll. The R.Hincll activity of this clone was 1, 000-fold that from H. influenzae Rc. The amino acid sequence of M.Hincll was compared with the sequences of four other adenine-specific type II methylases. Important homology was found between the M.Hincll and these other methylases.