Cloning, nucleotide sequence, and expression of the HincII restriction-modification system

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Restriction-modification systems are crucial for bacterial defense and DNA manipulation.
• Haemophilus influenzae Rc possesses the HincII restriction-modification system.

Purpose of the Study:

• To clone and express the genes encoding the HincII restriction endonuclease and methylase.
• To determine the DNA sequences of these genes.
• To characterize the expressed enzymes and compare the methylase sequence with known enzymes.

Main Methods:

• Gene cloning and expression in Escherichia coli RR1.
• DNA sequencing to determine gene length and predict protein sequences.
• Enzyme activity assays to quantify endonuclease production.
• Amino acid sequence comparison using bioinformatics tools.

Main Results:

• The HincII methylase (M.HincII) gene is 1,506 bp, encoding a 502-amino acid protein.
• The HincII endonuclease (R.HincII) gene is 774 bp, encoding a 258-amino acid protein.
• The genes overlap by 1 bp and are expressed in E. coli RR1-Hinc, leading to 1,000-fold increased R.HincII activity.
• M.HincII shows significant homology to other adenine-specific type II methylases.

Conclusions:

• The HincII methylase and endonuclease genes have been successfully cloned, sequenced, and expressed.
• The E. coli RR1-Hinc clone is a valuable tool for overproducing active HincII endonuclease.
• The sequence homology suggests conserved functional domains among adenine-specific type II methylases.