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V T Chu

Publications and source records attributed to V T Chu.

6 recordsLinked to original sources
PubMed2001

Control of branch-site choice by a group II intron.

The branch site of group II introns is typically a bulged adenosine near the 3'-end of intron domain 6. The branch site is chosen with extraordinarily high fidelity, even when the adenosine is mutated to other bases or if the typically bulged adenosine is paired. Given these facts, it has been difficult to discern the mechanism by which the proper branch site is chosen. In order to dissect the determinants for branch-point recognition, new mutations were introduced in the vicinity of the branch site and surrounding domains. Single mutations did not alter the high fidelity for proper branch-site selection. However, several combinations of mutations moved the branch site systematically to new positions along the domain 6 stem. Analysis of those mutants, together with a new alignment of domain 5 and domain 6 sequences, reveals a set of structural determinants that appear to govern branch-site selection by group II introns.

Base Sequence↗
PubMed2001

Acute management of dengue shock syndrome: a randomized double-blind comparison of 4 intravenous fluid regimens in the first hour.

Dengue hemorrhagic fever is an important cause of morbidity among Asian children, and the more severe dengue shock syndrome (DSS) causes a significant number of childhood deaths. DSS is characterized by a massive increase in systemic capillary permeability with consequent hypovolemia. Fluid resuscitation is critical, but as yet there have been no large trials to determine the optimal fluid regimen. We undertook a randomized blinded comparison of 4 fluids (dextran, gelatin, lactated Ringer's, and "normal" saline) for initial resuscitation of 230 Vietnamese children with DSS. All the children survived, and there was no clear advantage to using any of the 4 fluids, but the longest recovery times occurred in the lactated Ringer's group. The most significant factor determining clinical response was the pulse pressure at presentation. A comparison of the colloid and crystalloid groups suggested benefits in children presenting with lower pulse pressures who received one of the colloids. Further large-scale studies, stratified for admission pulse pressure, are indicated.

Adolescent↗
PubMed1998

Group II intron splicing in vivo by first-step hydrolysis.

Group I, group II and spliceosomal introns splice by two sequential transesterification reactions. For both spliceosomal and group II introns, the first-step reaction occurs by nucleophilic attack on the 5' splice junction by the 2' hydroxyl of an internal adenosine, forming a 2'-5' phosphodiester branch in the intron. The second reaction joins the two exons with a 3'-5' phosphodiester bond and releases intron lariat. In vitro, group II introns can self-splice by an efficient alternative pathway in which the first-step reaction occurs by hydrolysis. The resulting linear splicing intermediate participates in normal second-step reactions, forming spliced exon and linear intron RNAs. Here we show that the group II intron first-step hydrolysis reaction occurs in vivo in place of transesterification in the mitochondria of yeast strains containing branch-site mutations. As expected, the mutations block branching, but surprisingly still allow accurate splicing. This hydrolysis pathway may have been a step in the evolution of splicing mechanisms.

Esterification↗
PubMed1998

More than one way to splice an RNA: branching without a bulge and splicing without branching in group II introns.

Domain 6 (D6) of group II introns contains a bulged adenosine that serves as the branch-site during self-splicing. In addition to this adenosine, other structural features in D6 are likely to contribute to the efficiency of branching. To understand their role in promoting self-splicing, the branch-site and surrounding nucleotides were mutagenized. Detailed kinetic analysis on the self-splicing efficiency of the mutants revealed several interesting features. First, elimination of the branch-site does not preclude efficient splicing, which takes place instead through a hydrolytic first step. Second, pairing of the branch-site does not eliminate branching, particularly if the adenosine is involved in a mispair. Third, the G-U pairs that often surround group II intron branch-points contribute to the efficiency of branching. These results suggest that there is a strong driving force for promoting self-splicing by group II introns, which employ a versatile set of different mechanisms for ensuring that splicing is successful. In addition, the behavior of these mutants indicates that a bulged adenosine per se is not the important determinant for branch-site recognition in group II introns. Rather, the data suggest that the branch-site adenosine is recognized as a flipped base, a conformation that can be promoted by a variety of different substructures in RNA and DNA.

Adenosine↗