Disease relevance of Bullet

• Remarkably, cleavage at the 5' splice site and lariat formation do not occur when the precursor contains a beta-thalassemia deletion removing the polypyrimidine stretch and AG dinucleotide at the 3' splice site [1].
• Images in clinical medicine. Bullet embolism [2].
• This lariat structure, which has been characterized for an adenovirus 2 major late transcript, has a branch point, with 2'-5' and 3'-5' phosphodiester bonds emanating from a single adenosine residue [3].
• Two essential splice lariat branchpoint sequences in one intron in a xeroderma pigmentosum DNA repair gene: mutations result in reduced XPC mRNA levels that correlate with cancer risk [4].
• Volumetric echocardiography using the Bullet method provides an accurate and noninvasive estimate of CO in anesthetized neonatal foals and warrants investigation in critically ill conscious foals [5].

High impact information on Bullet

• Splicing occurs via a lariat intermediate whose branch site A residue is predicted to bulge from a duplex formed with the low abundance U12 small nuclear ribonucleoprotein (snRNP), which we confirm by psoralen cross-linking [6].
• We have isolated seven alleles of PRP16 that, like the original allele prp16-1, allow splicing of introns with a mutant branch site (UACUAAC to UACUACC), by forming lariat intermediates at the mutant C nucleotide [7].
• Processing of dead-end lariat intermediates to mRNA correlates with base pairing between U5 and the first two bases in exon 2 [8].
• We show that incubation of the intron lariat with ligated exons bE1 and bE2 leads to a complete reversal of the splicing reaction [9].
• When incubated with a foreign RNA species bearing a sequence motif that is complementary to exon binding site 1, the lariat can integrate into this RNA with the position of insertion immediately downstream of this sequence [9].

Biological context of Bullet

• Several mutations next to the branch point and in other parts of the core structure of group II introns are shown to affect lariat formation [10].
• Two other products, the spliced exons and the broken form of the lariat, were also characterized [11].
• Mutations in the sequence facing the branch point also allow residual lariat formation; however, free 3' exons are generated with false 5' termini, all of which are within a UCACA consensus sequence located upstream or downstream of the normal 3' splice site [12].
• We propose that decreasing the rate of ATP hydrolysis by Prp16 allows aberrantly formed lariat intermediates more time to proceed through the productive rather than the discard branch of this pathway [7].
• Analysis of messenger RNA splicing in yeast and in metazoa has led to the identification of an RNA molecule in a lariat conformation [13].

Anatomical context of Bullet

• SF2 is a 33 kd protein factor required for 5' splice site cleavage and lariat formation during pre-mRNA splicing in HeLa cell extracts [14].
• Excision of introns from nuclear precursors to messenger RNAs (pre-mRNAs) by the spliceosome requires two distinct phosphodiester transfer (transesterification) reactions: exchange of a 3'-5' for a 2'-5' bond in the first step (lariat formation) and exchange of one 3'-5' phosphodiester for another in the second step (exon ligation) [15].
• The self-splicing bl1 intron lariat from mitochondria of Saccharomyces cerevisiae catalyzed the insertion of nucleotidyl monomers derived from the 3' end of a donor RNA into an acceptor RNA in a 3' to 5' direction in vitro [16].
• Lariat formation has been studied intensively only with a few self-splicing group II introns, and little is known about how the numerous diverse introns in plant organelles are excised [17].
• The splicing of messenger RNA precursors (pre-mRNA) of eukaryotic cells involves the formation of a branched RNA intermediate known as a RNA lariat [18].

Associations of Bullet with other chemical compounds

• The excised introns of pre-mRNAs and intron-containing splicing intermediates are in a lariat configuration in which the 5' end of the intron is linked by a 2'-5' phosphodiester bond (RNA branch) to a single adenosine residue near the 3' end of the intron [19].
• The reaction results in lariat formation, concomitant with exon-exon ligation and does not require a guanosine nucleotide for its initiation [20].
• Using truncated precursor RNAs containing only the exon 3 to exon 4 region of the CALC-I gene it was shown that CT splicing is an inefficient reaction in which a uridine residue serves as the major site of lariat formation [21].
• In vitro self-splicing of Chs.psbA1 occurred via a lariat, and required Mg(2+) (>12 mM) and NH(4)(+) [22].
• During the splicing of introns out of pre-mRNA, the 2'-OH of the bulged adenine participates in the transesterification reaction at the 5'-exon and forms the branch-point residue of the lariat intermediate [23].

Gene context of Bullet

• Here we show that dsRNA stem-loop structures found in intronic regions of the S. cerevisiae RPS22B and RPL18A transcripts trigger degradation of unspliced pre-mRNAs and lariat introns and can control the level of mRNA produced from these intron-containing genes [24].
• In vitro and in vivo experiments indicated that snR39 is normally processed from the lariat of RPL7A, suggesting that the expressions of RPL7A and snR39 are linked [25].
• Saccharomyces cerevisiae Prp43 is a DEAH-box RNA-dependent ATPase that catalyzes the release of excised lariat intron from the mRNA spliceosome [26].
• This is the first example of a splicing defect due to a mutation in the lariat BPS in an intron of NPC1 found in NPC patients [27].
• Using modified substrates to either mutationally or chemically block the second step, we found that the association of Prp22p with the lariat intermediate represents an authentic transient intermediate and appears to be restricted to the last eight intron nucleotides [28].

Analytical, diagnostic and therapeutic context of Bullet

• SF1, SF2, and SF4B appear to be required for cleavage of the pre-mRNA at the 5' splice site and lariat formation, whereas SF3 and SF4A are only required for cleavage at the 3' splice site and exon ligation [29].
• Protein blots probed with labeled mRNA precursors either containing or lacking an intact 3' splice site reveal that the 70 kd polypeptide can bind pre-mRNA after immobilization on nitrocellulose and that it shows a preference for sequences located between the 3' splice junction and the site of lariat formation [30].
• Together, the results of Northern, ribozyme, RT-PCR, and lariat debranching analyses indicate that the two species are circular and linear RNAs of similar length and abundance [31].
• Sequence analysis of these genomic clones revealed that the two short segments specific for the two mRNAs are tandemly arranged in a genomic sequence and form exonic sequences equipped with AG and GT sequences on their 5' and 3' ends, respectively, and the putative consensus sequences for the lariat formation [32].
• The method was applied to a series of lariat ethers that were synthesized as ion-selective reagents for ion-selective electrodes [33].

References