Metal ion catalysis during group II intron self-splicing: parallels with the spliceosome

The identical reaction pathway executed by the spliceosome and self-splicing group II intron ribozymes has prompted the idea that both may be derived from a common molecular ancestor. The minimal sequence and structural similarities between group II introns and the spliceosomal small nuclear RNAs, h...

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Bibliographic Details
Published inGenes & development Vol. 13; no. 13; pp. 1729 - 1741
Main Authors Sontheimer, E J, Gordon, P M, Piccirilli, J A
Format Journal Article
LanguageEnglish
Published United States Cold Spring Harbor Laboratory Press 01.07.1999
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Summary:The identical reaction pathway executed by the spliceosome and self-splicing group II intron ribozymes has prompted the idea that both may be derived from a common molecular ancestor. The minimal sequence and structural similarities between group II introns and the spliceosomal small nuclear RNAs, however, have left this proposal in question. Mechanistic comparisons between group II self-splicing introns and the spliceosome are therefore important in determining whether these two splicing machineries may be related. Here we show that 3'-sulfur substitution at the 5' splice site of a group II intron causes a metal specificity switch during the first step of splicing. In contrast, 3'-sulfur substitution has no significant effect on the metal specificity of the second step of cis-splicing. Isolation of the second step uncovers a metal specificity switch that is masked during the cis-splicing reaction. These results demonstrate that group II intron ribozymes are metalloenzymes that use a catalytic metal ion for leaving group stabilization during both steps of self-splicing. Furthermore, because 3'-sulfur substitution of a spliceosomal intron has precisely the same effects as were observed during cis-splicing of the group II intron, these results provide striking parallels between the catalytic mechanisms employed by these two systems.
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Present address: Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208-3500 USA.
Corresponding author.E-MAIL jpicciri@midway.uchicago.edu; FAX (773) 702-3611.
ISSN:0890-9369
DOI:10.1101/gad.13.13.1729