Insertion of a homing endonuclease creates a genes-in-pieces ribonucleotide reductase that retains function.
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.
Friedrich
Nancy C
NC
Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada N6A 1C7.
Torrents
Eduard
E
Gibb
Ewan A
EA
Sahlin
Margareta
M
Sjöberg
Britt-Marie
BM
Edgell
David R
DR
D016980:Aeromonas hydrophila / Q000821:virology; D000595:Amino Acid Sequence; D001435:Bacteriophages / Q000235:genetics*; D001483:Base Sequence; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics*; D004251:DNA Transposable Elements / Q000235:genetics*; D004926:Escherichia coli; D005814:Genes, Viral / Q000235:genetics*; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000235:genetics* / Q000378:metabolism; D009841:Oligonucleotides / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012262:Ribonucleoside Diphosphate Reductase / Q000235:genetics*; D017422:Sequence Analysis, DNA
D015280:DNA Restriction-Modification Enzymes; D004251:DNA Transposable Elements; D046912:Multiprotein Complexes; D009841:Oligonucleotides; D012262:Ribonucleoside Diphosphate Reductase