RNA-directed amino acid coupling as a model reaction for primitive coded translation.

The stereochemical theory claims that primitive coded translation initially occurred in the RNA world by RNA-directed amino acid coupling. In this study, we show that the HIV Tat aptamer RNA is capable of recognizing two consecutive arginine residues within the Tat peptide, thus demonstrating how RNA might be able to position two amino acids for sequence-specific coupling. We also show that this RNA can act as a template to accelerate the coupling of a single arginine residue to the N-terminal arginine residue of a peptide primer. The results might have implications for our understanding of the origin of translation.

Validation of a Cox prognostic model for tooth autotransplantation.

OBJECTIVES: This study aimed to validate our Cox proportional hazards prognostic model for autotransplantation of teeth with complete root formation using prognostic index (PI) and determine whether the prognosis can be predicted. PATIENTS AND METHODS: The Protocol group, as a training data set for validation, consisted of 259 autotransplanted teeth to create a PI using the Cox model, as described previously. The Pre-protocol group, as the first validation data set, consisted of 95 autotransplanted teeth treated without a protocol. The Post-protocol group, as the second validation data set, consisted of 61 autotransplanted teeth obtained after the establishment of the prognostic model. Because four prognostic factors, including history of root canal treatment (yes), number of roots (multirooted), source of donor tooth (maxillary tooth), and duration of edentulism (≥2.5 months), were selected as a Cox prognostic model, 16 patterns of PI were constructed. First, the autotransplantated teeth in the Protocol group were divided into low- and high-risk groups respectively according to the median of PI as the cutoff value. The survival curves of low- and high-risk groups were calculated using the Kaplan-Meier method and tested using the log-rank test. Then, in the Pre- and Post-protocol groups, all transplanted teeth were divided into low-and high-risk teeth by the median of PI and the survival curves of low- and high- risk teeth were analyzed statistically in a similar manner. RESULTS: The survival curves of the low- and high-risk groups diverged significantly in the Protocol and Post-protocol groups. In the Pre-protocol group, the curves of the low- and high-risk groups were separated, and the low-risk survival rate was improved. CONCLUSIONS: Our Cox prognostic model for autotransplantation of teeth with complete root formation was useful in predicting the prognosis by external validation using PI.

Prognostic factors for autotransplantation of teeth with complete root formation.

OBJECTIVES: The aim of the present study was to evaluate the factors affecting the prognosis of the autotransplantation of teeth with complete root formation. STUDY DESIGN: A total of 259 transplanted teeth were studied. The significance of each of the prognostic factors was examined in 2 ways, first in a univariate analysis and then in a multivariate analysis. The comprehensive risk combining these factors that remained after multivariate analysis was calculated. RESULTS: Among 259 transplanted teeth, 27 (10.4%) were judged as unsuccessful cases. In the multivariate analysis, history of root canal treatment of donor tooth, multirooted, maxillary tooth as a donor, and duration of tooth absence at recipient site remained significantly associated with unsuccessful transplantation. Multifarious combination of the significant prognostic factors can decrease the comprehensive risk. CONCLUSIONS: Minimizing the comprehensive risk by combining significant prognostic factors improved the prognosis of autotransplantation of teeth with complete root formation.

An isostructural G-G to A-A substitution within the HIV RRE RNA switches the specificity towards arginine-rich peptides.

The HIV Rev protein utilizes a short alpha-helical arginine-rich RNA-binding domain to bind deeply within the major groove of an internal loop region of the Rev-response element (RRE) RNA. A G48-G71 base-pair which covaries to an isostructural A48-A71 base pair has been shown to play an important structure role in Rev-RRE binding. On the other hand, a high affinity RRE-binding peptide aptamer, the K1 peptide, was shown to have low binding affinity towards the RRE A48-A71 mutant, suggesting that the K1 peptide was recognizing the G48-G71 base-pair. In this study, in an attempt to understand the basis for the recognition of the G48-G71 base-pair by the K1 peptide, the selection of peptides that bind to the RRE A48A71 (RREAA) mutant was carried out. As a result, a peptide specific for the mutant, the LDN1 peptide, was identified. The LDN1 peptide was found to bind to the internal loop region of the RREAA, as in the case of the K1-RRE interaction. However, amino acids important for LDN1-binding to RREAA, were found to be distinct from those important for K1-binding to the RRE. These results demonstrate how subtle changes in RNA structure can dramatically alter the peptide-binding specificity of an RNA.