Assembly of a fragmented ribonucleotide reductase by protein interaction domains derived from a mobile genetic element.
Ribonucleotide reductase (RNR) is a critical enzyme of nucleotide metabolism, synthesizing precursors for DNA replication and repair. In prokaryotic genomes, RNR genes are commonly targeted by mobile genetic elements, including free standing and intron-encoded homing endonucleases and inteins. Here, we describe a unique molecular solution to assemble a functional product from the RNR large subunit gene, nrdA that has been fragmented into two smaller genes by the insertion of mobE, a mobile endonuclease. We show that unique sequences that originated during the mobE insertion and that are present as C- and N-terminal tails on the split NrdA-a and NrdA-b polypeptides, are absolutely essential for enzymatic activity. Our data are consistent with the tails functioning as protein interaction domains to assemble the tetrameric (NrdA-a/NrdA-b)(2) large subunit necessary for a functional RNR holoenzyme. The tails represent a solution distinct from RNA and protein splicing or programmed DNA rearrangements to restore function from a fragmented coding region and may represent a general mechanism to neutralize fragmentation of essential genes by mobile genetic elements.
Crona
Mikael
M
Department of Molecular Biology and Functional Genomics, Stockholm University, S-10691 Stockholm, Sweden.
Moffatt
Connor
C
Friedrich
Nancy C
NC
Hofer
Anders
A
Sjöberg
Britt-Marie
BM
Edgell
David R
DR
D001435:Bacteriophages / Q000201:enzymology; D020134:Catalytic Domain; D019281:Dimerization; D020035:Holoenzymes / Q000235:genetics; D020071:Interspersed Repetitive Sequences; D009154:Mutation; D054730:Protein Interaction Domains and Motifs; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
D020035:Holoenzymes; D012264:Ribonucleotide Reductases