Very small mobile repeated elements in cyanobacterial genomes.
Mobile DNA elements play a major role in genome plasticity and other evolutionary processes, an insight gained primarily through the study of transposons and retrotransposons (generally approximately 1000 nt or longer). These elements spawn smaller parasitic versions (generally >100 nt) that propagate through proteins encoded by the full elements. Highly repeated sequences smaller than 100 nt have been described, but they are either nonmobile or their origins are not known. We have surveyed the genome of the multicellular cyanobacterium, Nostoc punctiforme, and its relatives for small dispersed repeat (SDR) sequences and have identified eight families in the range of from 21 to 27 nucleotides. Three of the families (SDR4, SDR5, and SDR6), despite little sequence similarity, share a common predicted secondary structure, a conclusion supported by patterns of compensatory mutations. The SDR elements are found in a diverse set of contexts, often embedded within tandemly repeated heptameric sequences or within minitransposons. One element (SDR5) is found exclusively within instances of an octamer, HIP1, that is highly over-represented in the genomes of many cyanobacteria. Two elements (SDR1 and SDR4) often are found within copies of themselves, producing complex nested insertions. An analysis of SDR elements within cyanobacterial genomes indicate that they are essentially confined to a coherent subgroup. The evidence indicates that some of the SDR elements, probably working through RNA intermediates, have been mobile in recent evolutionary time, making them perhaps the smallest known mobile elements.
Elhai
Jeff
J
Center for the Study of Biological Complexity and the Department of Biology, Virginia Commonwealth University, Richmond, Virginia 23284, USA. elhaij@vcu.edu
Kato
Michiko
M
Cousins
Sarah
S
Lindblad
Peter
P
Costa
José Luis
JL
D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D000458:Cyanobacteria / Q000235:genetics*; D016680:Genome, Bacterial; D020071:Interspersed Repetitive Sequences / Q000235:genetics*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D032041:Nested Genes; D009690:Nucleic Acid Conformation; D010802:Phylogeny
D001426:Bacterial Proteins