Slow formation of stable complexes during coincubation of minimal rRNA and ribosomal protein S4
Mayerle M, Bellur DL, Woodson SA.
Ribosomal protein S4 binds and stabilizes a five-helix junction or five-way junction (5WJ) in the 5' domain of 16S... more Ribosomal protein S4 binds and stabilizes a five-helix junction or five-way junction (5WJ) in the 5' domain of 16S ribosomal RNA (rRNA) and is one of two proteins responsible for nucleating 30S ribosome assembly. Upon binding, both protein S4 and 5WJ reorganize their structures. We show that labile S4 complexes rearrange into stable complexes within a few minutes at 42 °C, with longer coincubation leading to an increased population of stable complexes. In contrast, prefolding the rRNA has a smaller effect on stable S4 binding. Experiments with minimal rRNA fragments show that this structural change depends only on 16S residues within the S4 binding site. SHAPE (selective 2'-hydroxyl acylation analyzed by primer extension) chemical probing experiments showed that S4 strongly stabilizes 5WJ and the helix (H) 18 pseudoknot, which become tightly folded within the first minute of S4 binding. However, a kink in H16 that makes specific contacts with the S4 N-terminal extension, as well as a right-angle motif between H3, H4, and H18, requires a minute or more to become fully structured. Surprisingly, S4 structurally reorganizes the 530-loop and increases the flexibility of H3, which is proposed to undergo a conformational switch during 30S assembly. These elements of the S4 binding site may require other 30S proteins to reach a stable conformation.
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mRNA Transcript Diversity Creates New Opportunities for Pharmacological Intervention
by Ryan Smith
Published in Molecular Pharmacology 02/07/2012
Most protein coding genes generate multiple RNA transcripts through alternative splicing, variable 3' and 5'UTRs, and... more Most protein coding genes generate multiple RNA transcripts through alternative splicing, variable 3' and 5'UTRs, and RNA editing. While drug design typically targets the main transcript, alternative transcripts can have profound physiological effects, encoding proteins with distinct functions or regulatory properties. Formation of these alternative transcripts is tissue-selective and context-dependent, creating opportunities for more effective and targeted therapies with reduced adverse effects. Moreover, genetic variation can tilt the balance of alternative versus constitutive transcripts or generate aberrant transcripts that contribute to disease risk. Additionally, environmental factors and drugs modulate RNA splicing, affording new opportunities for the treatment of splicing disorders. For example, therapies targeting specific mRNA transcripts with splice-site directed oligonucleotides that correct aberrant splicing are already in clinical trials for genetic disorders such as Duchenne muscular dystrophy. High-throughput sequencing technologies facilitate discovery of novel RNA transcripts and protein isoforms, with applications ranging from neuromuscular disorders to cancer. Consideration of a gene’s transcript diversity should become an integral part of drug design, development, and therapy.
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Seen by:Behavior of RNAs transcripts during nucleolus assembly and disassembly in Vicia faba root meristematic cells under normal conditions and after colchicine treatment
To study the behavior of newly synthesized RNA molecules during unperturbed mitosis and after induction of aneuploid... more To study the behavior of newly synthesized RNA molecules during unperturbed mitosis and after induction of aneuploid nuclei, a novel method based on the incorporation of 5-ethynyl uridine was applied. This approach allows revealing transcription in cytological specimens by omitting immunocytochemical procedures. The obtained results indicate that RNAs synthesized in the preceding cell cycle behave similarly as nucleolar proteins and participate in post-mitotic nucleolar assembly not only during unperturbed nuclear divisions. Colocalization of nucleolar proteins and RNAs seems also to occur in aneuploid nuclei devoid of functional nucleolar organizer regions (NORs) or NOR per se. This paper also shows the presence of nucleoplasmic gene expression in aberrant aneuploid nuclei and micronuclei, despite occurrence of their genetic material disorganization. Moreover, experiments showing the effect of transcription and replication inhibition on the induction of aneuploid nuclei were also performed. Presented data shed new light on nucleologenesis and co-existence of nucleolar proteins with RNAs in prenucleolar bodies formed in aneuploid nuclei devoid of functional NORs.

