On the basis of sequence similarities, the following bacterial and eukaryotic
proteins seem to form a family:
Escherichia coli and related bacteria ribonuclease II (EC 22.214.171.124) (RNase
II) (gene rnb) . RNase II is an exonuclease involved in mRNA decay. It
degrades mRNA by hydrolyzing single-stranded polyribonucleotides
processively in the 3' to 5' direction.
Bacterial ribnuclease R , a 3'-5'exoribonuclease that participates in an
essential cell function.
Yeast protein SSD1 (or SRK1) which is implicated in the control of the cell
cycle G1 phase.
Yeast protein DIS3 , which binds to ran (GSP1) and ehances the the
nucleotide-releasing activity of RCC1 on ran.
Fission yeast protein dis3, which is implicated in mitotic control.
Neurospora crassa cyt-4, a mitochondrial protein required for RNA 5' and 3'
end processing and splicing.
Yeast protein MSU1, which is involved in mitochondrial biogenesis.
Synechocystis strain PCC 6803 protein zam , which control resistance to
the carbonic anhydrase inhibitor acetazolamide.
Caenorhabditis elegans hypothetical protein F48E8.6.
The size of these proteins range from 644 residues (rnb) to 1250 (SSD1). While
their sequence is highly divergent they share a conserved domain in their C-terminal section . It is possible that this domain plays a role in a
putative exonuclease function that would be common to all these proteins. We
have developed a signature pattern based on the core of this conserved domain.
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