@article {405,
	title = {A tyrosyl-tRNA synthetase suppresses structural defects in the two major helical domains of the group I intron catalytic core.},
	journal = {J Mol Biol},
	volume = {262},
	number = {2},
	year = {1996},
	month = {1996 Sep 20},
	pages = {87-104},
	abstract = {The Neurospora crassa mitochondrial tyrosyl-tRNA synthetase, the CYT-18 protein, functions in splicing group I introns by promoting the formation of the catalytically active structure of the intron RNA. The group I intron catalytic core is thought to consist of two extended helical domains, one formed by coaxial stacking of P5, P4, P6, and P6a (P4-P6 domain) and the other consisting of P8, P3, P7, and P9 (P3-P9 domain). To investigate how CYT-18 stabilizes the active RNA structure, we used an Escherichia coli genetic assay based on the phage T4 td intron to systematically test the ability of CYT-18 to compensate for structural defects in three key regions of the catalytic core: J3/4 and J6/7, connecting regions that form parts of the triple-helical-scaffold structure with the P4-P6 domain, and P7, a long-range base-pairing interaction that forms the guanosine-binding site and is part of the P3-P9 domain. Our results show that CYT-18 can suppress numerous mutations that disrupt the J3/4 and J6/7 nucleotide-triple interactions, as well as mutations that disrupt base-pairing in P7. CYT-18 suppressed mutations of phylogenetically conserved nucleotide residues at all positions tested, except for the universally conserved G-residue at the guanosine-binding site. Structure mapping experiments with selected mutant introns showed that the CYT-18-suppressible J3/4 mutations primarily impaired folding of the P4-P6 domain, while the J6/7 mutations impaired folding of both the P4-P6 and P3-P9 domains to various degrees. The P7 mutations impaired the formation of both P7 and P3, thereby grossly disrupting the P3-P9 domain. The finding that the P7 mutations also impaired formation of P3 provides evidence that the formation of these two long-range pairings is interdependent in the td intron. Considered together with previous work, the nature of mutations suppressed by CYT-18 supports a model in which CYT-18 helps assemble the P4-P6 domain and then stabilizes the two major helical domains of the catalytic core in the correct relative orientation to form the intron{\textquoteright}s active site.},
	keywords = {Bacteriophage T4, Base Sequence, Chromosome Mapping, Escherichia coli, Introns, Kinetics, Mitochondria, Molecular Sequence Data, Mutagenesis, Site-Directed, Neurospora crassa, Nucleic Acid Conformation, Phenotype, RNA Splicing, RNA, Viral, Tyrosine-tRNA Ligase},
	issn = {0022-2836},
	doi = {10.1006/jmbi.1996.0501},
	author = {Myers, C A and Wallweber, G J and Rennard, R and Kemel, Y and Caprara, M G and Mohr, G and Lambowitz, A M}
}
