Defining the protein complexome of translation termination factor eRF1: Identification of four novel eRF1-containing complexes that range from 20S to 57S in size

Cloning of TaeRF1 gene from Caucasian clover and its functional analysis responding to low-temperature stress

Low temperature (LT) is an important threat to the normal growth of plants. In this study, based on the full-length transcriptome sequencing results, the cold resistance genes were cloned from Caucasian clover with strong cold resistance. We cloned the CDS of TaeRF1, which is 1311 bp in length and encodes 436 amino acids. The molecular weight of the protein is 48.97 kDa, which had no transmembrane structure, and its isoelectric point (pI) was 5.42. We predicted the structure of TaeRF1 and found 29 phosphorylation sites. Subcellular localization showed that TaeRF1 was localized and expressed in cell membrane and chloroplasts. The TaeRF1 gene was induced by stress due to cold, salt, alkali and drought and its expression level was higher in roots and it was more sensitive to LT. Analysis of transgenic A. thaliana plants before and after LT treatment showed that the TaeRF1 gene enhanced the removal of excess H₂O₂, and increased the activity of antioxidant enzymes, thus improving the plant's ability to resist stress. Additionally, the OE lines showed increased cold tolerance by upregulating the transcription level of cold-responsive genes (CBF1, CBF2, COR15B, COR47, ICE1, and RD29A). This study demonstrates that TaeRF1 is actively involved in the responses of plants to LT stress. We also provide a theoretical basis for breeding and a potential mechanism underlying the responses of Caucasian clover to abiotic stress.

The non-prion SUP35 preexists in large chaperone-containing molecular complexes

Prions, misfolded proteins that aggregate, cause an array of progressively deteriorating conditions to which, currently, there are no effective treatments. The presently accepted model indicates that the soluble non-prion forms of prion-forming proteins, such as the well-studied SUP35, do not exist in large aggregated molecular complexes. Here, we show using analytical ultracentrifugation with fluorescent detection that the non-prion form of SUP35 exists in a range of discretely sized soluble complexes (19S, 28S, 39S, 57S, and 70S-200S). Similar to the [PSI+] aggregated complexes, each of these [psi-] complexes associates at stoichiometric levels with a large variety of molecular chaperones: HSP70 proteins comprise the major component. Another yeast prion-forming protein, RNQ1 (known to promote the production of the prion SUP35 state), is also present in SUP35 complexes. These results establish that the non-prion SUP35, like its prion form, is predisposed to form large molecular complexes containing chaperones and other prion-forming proteins. These results agree with our previous studies on the huntingtin protein. That the normal forms for aggregation-prone proteins may preexist in large molecular complexes has important ramifications for the progression of diseases involving protein aggregation.

Identification of a 57S translation complex containing closed-loop factors and the 60S ribosome subunit

In eukaryotic translation the 60S ribosome subunit has not been proposed to interact with mRNA or closed-loop factors eIF4E, eIF4G, and PAB1. Using analytical ultracentrifugation with fluorescent detection system, we have identified a 57S translation complex that contains the 60S ribosome, mRNA, and the closed-loop factors. Previously published data by others also indicate the presence of a 50S-60S translation complex containing these same components. We have found that the abundance of this complex increased upon translational cessation, implying formation after ribosomal dissociation. Stoichiometric analyses of the abundances of the closed-loop components in the 57S complex indicate this complex is most similar to polysomal and monosomal translation complexes at the end of translation rather than at the beginning or middle of translation. In contrast, a 39S complex containing the 40S ribosome bound to mRNA and closed-loop factors was also identified with stoichiometries most similar to polysomal complexes engaged in translation, suggesting that the 39S complex is the previously studied 48S translation initiation complex. These results indicate that the 60S ribosome can associate with the closed-loop mRNA structure and plays a previously undetected role in the translation process.