Mechanism of recycling of post-termination ribosomal complexes in eubacteria: a new role of initiation factor 3.

Ribosome recycling is a process which dissociates the post-termination complexes (post-TC) consisting of mRNA-bound ribosomes harbouring deacylated tRNA(s). Ribosome recycling factor (RRF), and elongation factor G (EFG) participate in this crucial process to free the ribosomal subunits for a new round of translation. We discuss the over-all pathway of ribosome recycling in eubacteria with especial reference to the important role of the initiation factor 3 (IF3) in this process. Depending on the step(s) at which IF3 function is implicated, three models have been proposed. In model 1, RRF and EFG dissociate the post-TCs into the 50S and 30S subunits, mRNA and tRNA(s). In this model, IF3, which binds to the 30S subunit, merely keeps the dissociated subunits apart by its anti-association activity. In model 2, RRF and EFG separate the 50S subunit from the post-TC. IF3 then dissociates the remaining complex of mRNA, tRNA and the 30S subunit, and keeps the ribosomal subunits apart from each other. However, in model 3, both the genetic and biochemical evidence support a more active role for IF3 even at the step of dissociation of the post-TC by RRF and EFG into the 50S and 30S subunits.

Expression change of TIF3 p36 at different stages of human bronchial epithelial cells transformed and induced by cadmium chloride / 中华劳动卫生职业病杂志

<p><b>OBJECTIVE</b>To explore the molecular mechanisms potentially responsible for carcinogenesis due to cadmium by detecting expression change of the translation initiation factor 3 (TIF3 p36) in those malignant transformation of human bronchial epithelial cell lines (16HBE) induced by cadmium chloride (CdCl(2)).</p><p><b>METHODS</b>The expression changes of TIF3 p36 were detected and analyzed at different stages of malignant cells (semi transformed cells, transformed cells and tumorigenic cells) induced by CdCl(2) solution with both reverse transcription PCR technique and sensitive fluorescent quantitative PCR assay.</p><p><b>RESULTS</b>Compared with non-transformed human bronchial epithelial cells, the results of fluorescent quantitative PCR assay showed that the semi-transformed cells, transformed cells and tumorigenic cells all expressed higher levels of TIF3 p36 mRNA (P < 0.01 or P < 0.05). As compared with the control cells, the TIF3 expressions at different stages of malignant transformation were 3.1 times, 5.9 times and 9.9 times higher respectively in the low dosage group of CdCl(2) (5 micromol/L); 7.1 times, 6.8 times and 14.8 times respectively in the middle dosage group of CdCl(2) (10 micromol/L); 3.6 times, 3.0 times and 9.1 times respectively in high of dose of CdCl(2) (15 micromol/L). These results showed that there was the positive correlation between overexpression levels of TIF3 p36 mRNA and the malignant degree of the cells, but they were not related to the dosages of cadmium.</p><p><b>CONCLUSION</b>There is significantly abnormal overexpression of TIF3 gene during malignant transformation of human bronchial epithelial cell line induced by cadmium chloride, and the TIF3 expression is associated with the malignant degree of the cells, which may be one of molecular mechanisms potentially responsible for the carcinogenesis due to cadmium.</p>

Abnormal expression of eukaryotic translation factors in malignant transformed human bronchial epithelial cells induced by crystalline nickel sulfide / 生物医学与环境科学（英文）

<p><b>OBJECTIVE</b>To study the oncogenic potential of mouse translation initiation factor 3 (TIF3) and elongation factor-1delta (TEF-1delta) in malignant transformed human bronchial epithelial cells induced by crystalline nickel sulfide (NiS).</p><p><b>METHODS</b>Abnormal expressions of human TIF3 and TEF-1delta genes in two kinds of NiS-transformed cells and NiS-tumorigenic cell lines were investigated and analyzed by the reverse transcript polymerase chain reaction (RT-PCR) and fluorescent quantitative polymerase chain reaction (FQ-PCR), respectively.</p><p><b>RESULTS</b>RT-PCR analysis primarily showed that both human TIF3 and TEF-1delta mRNA expressions in two kinds of NiS-transformed cells and NiS-tumorigenic cell lines were increased as compared with controls. FQ-PCR assay showed that the levels of TIF3 expressions in the transformed cells and tumorigenic cells were 3 and 4 times higher respectively, and the elevated expressions of TEF-1delta cDNA copies were 2.7- to 3.5-fold in transformed cells and 4.1- to 5.2-fold in tumorigenic cells when compared with non-transformed cells, indicating that the over-expressions of human TIF3 and TEF-1delta genes were related to malignant degree of the cells induced by nickel.</p><p><b>CONCLUSIONS</b>These findings demonstrate that there are markedly abnormal expressions of TIF3 and TEF-1delta genes during malignant transformation of human bronchial epithelial cell lines induced by crystalline NiS. They seem to be the molecular mechanisms potentially responsible for human carcinogensis due to nickel.</p>