Biochemistry

An Endonuclease Tango

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Science  22 Aug 2008:
Vol. 321, Issue 5892, pp. 1020
DOI: 10.1126/science.321.5892.1020a

The degradation of mRNA transcripts is an important cellular mechanism contributing to the regulation of gene expression. In Escherichia coli, the first step of this process involves internal cleavage of mRNA into fragments by the endoribonuclease RNase E. The structure of the RNase E catalytic domain in complex with short RNA substrates revealed a tetramer in which RNA is bound by two sub-domains of one monomer and cleaved at the catalytic site of another monomer. Koslover et al. have determined the structure of the unliganded RNase E catalytic domain and discovered large conformational differences relative to the substrate-bound protein. In the unliganded structure, the two subdomains of each monomer that furnish the RNA binding residues (shown in space-filling representation) are rotated away from the rest of the monomer and from the neighboring catalytic site by about 60°, which allows the substrate easy access. Pivoting then carries the RNA into close proximity to the catalytic site. In addition, the quaternary structure of the tetramer is substantially reorganized in unliganded RNase E, suggesting a high degree of structural flexibility that may permit the enzyme to accommodate RNA molecules of various sizes and shapes by using different combinations of binding and catalytic sites within the tetramer. — NM*

Structure 16, 1238 (2008).

  • * Nilah Monnier is a summer intern in Science's editorial department.

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