This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pinarbasi, H. Articles by Hornby, D. P. Search for Related Content PubMed PubMed Citation Articles by Pinarbasi, H. Articles by Hornby, D. P.

The Small Subunit of M · AquI Is Responsible for Sequence-Specific DNA Recognition and Binding in the Absence of the Catalytic Domain

Department of Biochemistry,¹ Department of Medical Biology and Genetics, Medicine Faculty, Cumhuriyet University, Sivas, Turkey,² Department of Molecular Biology and Biotechnology, Sheffield University, Sheffield, United Kingdom³

Received 12 August 2002/ Accepted 16 November 2002

AquI DNA methyltransferase (M · AquI) catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to the C5 position of the outermost deoxycytidine base in the DNA sequence 5'-CCCGGG-3'. M · AquI is a heterodimer in which the polypeptide chain is separated at the junction between the two equivalent structural domains in the related enzyme M · HhaI. Recently, we reported the subcloning, overexpression, and purification of the subunits ( and ß) of M · AquI separately. Here we describe the DNA binding properties of M · AquI. The results presented here indicate that the ß subunit alone contains all of the information for sequence-specific DNA recognition and binding. The first step in the sequence-specific recognition of DNA by M · AquI involves the formation of binary complex with the target recognition domain in conjunction with conserved sequence motifs IX and X, found in all known C5 DNA methyltransferases, contained in the ß subunit. The subunit enhances the binding of the ß subunit to DNA specifically and nonspecifically. It is likely that the addition of the subunit to the ß subunit stabilizes the conformation of the ß subunit and thereby enhances its affinity for DNA indirectly. Addition of S-adenosyl-L-methionine and its analogues S-adenosyl-L-homocysteine and sinefungin enhances binding, but only in the presence of the subunit. These compounds did not have any effect on DNA binding by the ß subunit alone. Using a 30-mer oligodeoxynucleotide substrate containing 5-fluorodeoxycytidine (5-FdC), it was found that the ß subunit alone did not form a covalent complex with its specific sequence in the absence or presence of S-adenosyl-L-methionine. However, the addition of the subunit to the ß subunit led to the formation of a covalent complex with specific DNA sequence containing 5-FdC.

This article has been cited by other articles:

• Loenen, W. A. M. (2003). Tracking EcoKI and DNA fifty years on: a golden story full of surprises. Nucleic Acids Res 31: 7059-7069 [Abstract] [Full Text]