Words similar to operons
Example sentences for: operons
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This approach had been pioneered in the classical work of Dobzhansky and Sturtevant who used inversions in Drosophila chromosomes to construct an evolutionary tree [ 12 ] . Subsequently, mathematical methods have been developed to calculate rearrangement distances between genomes, and, using these, phylogenetic trees have been built for certain small genomes, such as plant mitochondria and herpesviruses [ 13 14 ] . These approaches, however, are applicable only to genomes that show significant conservation of global gene order, which is manifestly not the case among prokaryotes [ 15 16 17 ] . Even relatively close species such as, for example, Escherichia coli and Haemophilus influenzae, two species of the γ-subdivision of Proteobacteria, retain very little conservation of gene order beyond the operon level (typically, two-to-four genes in a row), and essentially none is detectable among evolutionarily distant bacteria and archaea [ 15 16 18 ] . Very few operons, primarily those coding for physically interacting subunits of multiprotein complexes such as certain ribosomal proteins or RNA-polymerase subunits, are conserved across a wide range of prokaryotic lineages [ 15 16 ] . On the other hand, pairwise comparisons of even distantly related prokaryotic genomes reveal considerable number of shared (predicted) operons, which creates an opportunity for a meaningful comparative analysis [ 19 ] [ 20 21 ] .
In Nostoc, tyrP1 (encoding tyrosinase) has been inserted between trpEa and trpEb . All other cyanobacteria, including Anabaena , lack tyrP1 . The two trp operons are less compact than frequently observed elsewhere, and relatively large intergenic spacing exists, especially in N. punctiforme . The only instance of translational coupling is between trpAa • trpAb and trpD in N. punctiforme .
The clustering of functionally related genes in prokaryotic genomes into co-transcribed and co-regulated units, operons, often allows functional assignments through the principle of 'guilt by association' [ 30 31 32 ] . Generally, genes whose products physically interact to form a complex or are involved in successive steps in a biochemical pathway form operons that are conserved over large evolutionary distances [ 30 ] . On previous occasions, we have used gene neighborhoods or operons to predict novel DNA repair complexes and their components [ 33 ] . Accordingly, a similar approach was applied to the three families of SSAPs (RecT/Redβ, ERF, Rad52), to shed light on their functional links.
Nematodes process many mRNAs by trans -splicing to SL1 and other splice leader sequences [ 57 58 ] and in C. elegans use of different splice leaders is tied to genome organization in operons [ 59 ] . SL1 is the predominant nematode splice leader and is highly conserved across many species.
This is in contrast to the regulatory logic of prokaryotes, in which the expression of defined sets of genes in operons is a predominant feature of regulation.
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