Eukaryotic precursor (pre)-tRNAs are processed at both ends prior to maturation. Pre-tRNAs and other nascent transcripts synthesized by RNA polymerase III are bound at their 3 ends at the sequence motif UUU OH [3 oligo(U)] by the La antigen, a conserved phosphoprotein whose role in RNA processing has been associated previously with 3-end maturation only. We show that in addition to its role in tRNA 3-end maturation, human La protein can also modulate 5 processing of pre-tRNAs. Both the La antigen's N-terminal RNA-binding domain and its C-terminal basic region are required for attenuation of pre-tRNA 5 processing. RNA binding and nuclease protection assays with a variety of pre-tRNA substrates and mutant La proteins indicate that 5 protection is a highly selective activity of La. This activity is dependent on 3 oligo(U) in the pre-tRNA for interaction with the N-terminal RNA binding domain of La and interaction of the C-terminal basic region of La with the 5 triphosphate end of nascent pre-tRNA. Phosphorylation of La is known to occur on serine 366, adjacent to the C-terminal basic region. We show that this modification interferes with the La antigen's ability to protect pre-tRNA i Met from 5 processing either by HeLa extract or purified RNase P but that it does not affect interaction with the 3 end of pre-tRNA. These findings provide the first evidence to indicate that tRNA 5-end maturation may be regulated in eukaryotes. Implications of triphosphate recognition is discussed as is a role for La phosphoprotein in controlling transcriptional and posttranscriptional events in the biogenesis of polymerase III transcripts.Studies of pre-tRNA processing in Escherichia coli have revealed that although the order of 5Ј and 3Ј processing events can vary among substrates, many eukaryotic precursor (pre)-tRNAs are processed in a preferred order (21). Classical eukaryotic tRNA genes are monocistronic and compared to most of their prokaryotic counterparts their primary transcripts are short and simple (18,33). Although many features of tRNA maturation, including 5Ј processing by RNase P, have been conserved from bacteria to humans, mechanisms of 3Ј-end maturation were not. Like other transcripts synthesized by RNA polymerase III (Pol III), pre-tRNAs are terminated at their 3Ј end by the sequence motif UUU OH , hereafter referred to as 3Ј oligo(U), which comprises a high-affinity binding site for the La protein (34). This oligo(U) tract, together with a short sequence stretch proximal to it, comprise the 3Ј trailer of eukaryotic pre-tRNAs which must be removed prior to enzymatic addition of CCA (8).Evolutionary conservation of La phosphoprotein and its interaction with 3Ј oligo(U) indicate the importance of this protein in the biogenesis of Pol III transcripts (38, 42). Indeed, La can modulate pre-tRNA 3Ј-end metabolism in Saccharomyces cerevisiae (43). Yeast cells can process pre-tRNA 3Ј ends by either exonuclease-or endonuclease-mediated pathways, and La can influence which pathway is used (43).La's involvement in RNA biogen...
The human La antigen is an RNA-binding protein that facilitates transcriptional termination and reinitiation by RNA polymerase III. Native La protein fractionates into transcriptionally active and inactive forms that are unphosphorylated and phosphorylated at serine 366, respectively, as determined by enzymatic and mass spectrometric analyses. Serine 366 comprises a casein kinase II phosphorylation site that resides within a conserved region in the La proteins from several species. RNA synthesis from isolated transcription complexes is inhibited by casein kinase II-mediated phosphorylation of La serine 366 and is reversible by dephosphorylation. This work demonstrates a novel mechanism of transcriptional control at the level of recycling of stable transcription complexes.
). Others have previously dissected the La protein into an N-terminal domain that binds RNA and a C-terminal domain that does not. Here, deletion and substitution mutants of La were examined for general RNA binding, RNA 3-end protection, and transcription factor activity. Although some La mutants altered in a C-terminal basic region bind RNA in mobility shift assays, they are defective in RNA 3-end protection and do not support transcription, while one C-terminal substitution mutant is defective only in transcription. Moreover, a Cterminal fragment lacking RNA binding activity appears able to support low levels of transcription by pol III. While efficient multiround transcription is supported only by mutants that bind RNA and contain a C-terminal basic region. These analyses indicate that RNA binding contributes to but is not sufficient for La transcription factor activity and that the C-terminal domain plays a role in transcription that is distinguishable from simple RNA binding. The transcription factor activity of La can be reversibly inhibited by RNA, suggesting the potential for feedback inhibition of pol III transcription.Eukaryotic RNA polymerase III (pol III) is responsible for synthesizing the abundant transcripts of tRNA, 5S rRNA, 7SL RNA, and U6 RNA genes as well as other small RNA genes (reviewed in reference 44). To produce a sufficient quantity of RNAs of the correct structure, transcription initiation and termination must be accurate and reinitiation must be efficient. pol III alone cannot accomplish this and must rely on transcription factors (TFs) that bind to control elements and direct RNA synthesis. The adenovirus-associated (VA1) RNA gene and cellular tRNA and Alu genes have internal promoters and 3Ј terminators that direct transcription by pol III. Mammalian TFIIIC1 and TFIIIC2 bind to the control elements of these genes (12, 43). After TFIIIB joins, the resulting preinitiation complex is stable and can be recycled for multiple rounds of transcription by pol III (5,21,27,43).Mammalian in vitro transcription assays have used reconstituted systems that contain at least one partially purified fraction. For example, mammalian TFIIIC2, TFIIIB, and pol III have been highly purified, while TFIIIC1 and TFIIIC1Ј represent relatively crude yet essential fractions (42, 43). In the Saccharomyces cerevisiae system, elegant studies have shown that recombinant or highly purified TFIIIB and TFIIIC are sufficient for multiround transcription (21), although it has also been reported that transcription can be stimulated by TFIIIE, a partially characterized fraction (13, 37). Thus, in both yeast and mammalian pol III systems, while the central factors required for in vitro transcription have been identified and continue to be characterized, evidence also suggests that ancillary, less well characterized factors may stimulate transcription. While remarkable progress has been made in understanding assembly of the preinitiation complex, relatively less effort has been directed toward understanding of the mechanism...
This study was conducted to investigate the effects of dietary arginine ( Arg ) supplementation on the inflammatory response and gut microbiota of broiler chickens subjected to Salmonella enterica serovar Typhimurium. One hundred and forty 1-day-old Arbor Acres male birds were randomly assigned to a 2 × 2 factorial arrangement including diet treatment (with or without 0.3% Arg supplementation) and immunological stress (with or without S. typhimurium challenge). Samples were obtained at 7 D after infection (day 23). Results showed that S. typhimurium challenge caused histopathological and morphological damages, but Arg addition greatly reduced these intestinal injuries. S. typhimurium challenge elevated the levels of serum inflammatory parameters, including diamine oxidase, C-reactive protein, procalcitonin, IL-1β, IL-8, and lipopolysaccharide-induced tumor necrosis factor-alpha factor ( LITNF ) homolog. However, Arg supplementation decreased the serum procalcitonin, IL-1β, IL-8, and LITNF concentration. S. typhimurium challenge significantly increased jejunal IL-1β , IL-8 , IL-10 , and IL-17 mRNA expression and tended to upregulate IL-22 mRNA expression, but Arg supplementation remarkably reduced IL-8 mRNA expression, tended to downregulate IL-22 mRNA expression, and dramatically elevated IFN-γ and IL-10 mRNA expression. In addition, sequencing data of 16S rDNA indicated that the population of Proteobacteria phylum; Enterobacteriaceae family; Escherichia–Shigella, and Nitrosomonas genera; and Escherichia coli and Ochrobactrum intermedium species were more abundant, but the population of Rhodocyclaceae and Clostridiaceae _ 1 families and Candidatus Arthromitus genus were less abundant in the ileal digesta of birds with only S. typhimurium infection when compared with the controls. Treatment with Arg in birds subjected to S. typhimurium challenge increased the abundances of Firmicutes phylum, Clostridiaceae _1 family, Methylobacterium and Candidatus Arthromitus genera but decreased the abundance of Nitrosomonas genus and Rhizobium cellulosilyticum and Rubrobacter xylanophilus species as compared with the only S. typhimurium –challenged birds. In conclusion, Arg supplementation can alleviate intestinal mucosal impairment by ameliorating inflammatory response and modulating gut microbiota in broiler chickens cha...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.