Metal ion interaction with cosubstrate in self-splicing of group I introns.
The catalytic mechanism for self-splicing of the group I intron in the pre-mRNA from the nrdB gene in bacteriophage T4 has been investigated using 2'-amino- 2'-deoxyguanosine or guanosine as cosubstrates in the presence of Mg2+, Mn2+and Zn2+. The results show that a divalent metal ion interacts with the cosubstrate and thereby influences the efficiency of catalysis in the first step of splicing. This suggests the existence of a metal ion that catalyses the nucleophilic attack of the cosubstrate. Of particular significance is that the transesterification reactions of the first step of splicing with 2'-amino-2'-deoxyguanosine as cosubstrate are more efficient in mixtures containing either Mn2+or Zn2+together with Mg2+than with only magnesium ions present. The experiments in metal ion mixtures show that two (or more) metal ions are crucial for the self-splicing of group I introns and suggest the possibility that more than one of these have a direct catalytic role. A working model for a two-metal-ion mechanism in the transesterification steps is suggested.
Sjögren
A S
AS
Department of Molecular Biology, Arrhenius Laboratory, Stockholm University, S-10691 Stockholm, Sweden.
Pettersson
E
E
Sjöberg
B M
BM
Strömberg
R
R
D017122:Bacteriophage T4 / Q000201:enzymology*; D002413:Cations, Divalent; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000378:metabolism; D006151:Guanosine / Q000378:metabolism; D007438:Introns; D008274:Magnesium / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology*; D012322:RNA Precursors; D012326:RNA Splicing; D012367:RNA, Viral; D012264:Ribonucleotide Reductases / Q000235:genetics*; D013379:Substrate Specificity; D014764:Viral Proteins / Q000235:genetics*; D015032:Zinc / Q000494:pharmacology*
D002413:Cations, Divalent; D012322:RNA Precursors; D012367:RNA, Viral; D014764:Viral Proteins; D006151:Guanosine; D008345:Manganese; C014319:2'-amino-2'-deoxyguanosine; D012264:Ribonucleotide Reductases; D003849:Deoxyguanosine; D008274:Magnesium; D015032:Zinc