Previous Article |
Table of Contents
| Next Article 
BIOLOGICAL SCIENCES / BIOCHEMISTRY
Insertion of a homing endonuclease creates a genes-in-pieces ribonucleotide reductase that retains function
,
*Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 1C7; and Department of Molecular Biology and Functional Genomics, Stockholm University, SE-10691 Stockholm, Sweden
Edited by Marlene Belfort, New York State Department of Health, Albany, NY, and approved February 13, 2007 (received for review November 9, 2006)
In bacterial and phage genomes, coding regions are sometimes interrupted by self-splicing introns or inteins, which can encode mobility-promoting homing endonucleases. Homing endonuclease genes are also found free-standing (not intron- or intein-encoded) in phage genomes where they are inserted in intergenic regions. One example is the HNH family endonuclease, mobE, inserted between the large (nrdA) and small (nrdB) subunit genes of aerobic ribonucleotide reductase (RNR) of T-even phages T4, RB2, RB3, RB15, and LZ7. Here, we describe an insertion of mobE into the nrdA gene of Aeromonas hydrophila phage Aeh1. The insertion creates a unique genes-in-pieces arrangement, where nrdA is split into two independent genes, nrdA-a and nrdA-b, each encoding cysteine residues that correspond to the active-site residues of uninterrupted NrdA proteins. Remarkably, the mobE insertion does not inactivate NrdA function, although the insertion is not a self-splicing intron or intein. We copurified the NrdA-a, NrdA-b, and NrdB proteins as complex from Aeh1-infected cells and also showed that a reconstituted complex has RNR activity. Class I RNR activity in phage Aeh1 is thus assembled from separate proteins that interact to form a composite active site, demonstrating that the mobE insertion is phenotypically neutral in that its presence as an intervening sequence does not disrupt the function of the surrounding gene.
bacteriophage Aeh1 | gene structure | intervening sequence
Present address: Institute for Bioengineering of Catalonia (IBEC) and Microbiology Department, Biology Faculty, Avinguda Diagonal 645, ES-08028 Barcelona, Spain.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0609915104/DC1.
To whom correspondence should be addressed. E-mail: dedgell{at}uwo.ca
© 2007 by The National Academy of Sciences of the USA
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg What's this?
This article has been cited by other articles in HighWire Press-hosted journals:
|
|
 |
|
  E. A. Gibb and D. R. Edgell Multiple Controls Regulate the Expression of mobE, an HNH Homing Endonuclease Gene Embedded within a Ribonucleotide Reductase Gene of Phage Aeh1 J. Bacteriol., July 1, 2007; 189(13): 4648 - 4661. [Abstract] [Full Text] [PDF]
|
|
