RNA

About: RNA is a research topic. Over the lifetime, 111695 publications have been published within this topic receiving 5475262 citations. The topic is also known as: ribonucleic acid.

A new yeast poly(A) polymerase complex involved in RNA quality control.

Abstract: Eukaryotic cells contain several unconventional poly(A) polymerases in addition to the canonical enzymes responsible for the synthesis of poly(A) tails of nuclear messenger RNA precursors. The yeast protein Trf4p has been implicated in a quality control pathway that leads to the polyadenylation and subsequent exosome-mediated degradation of hypomethylated initiator tRNAMet (tRNAiMet). Here we show that Trf4p is the catalytic subunit of a new poly(A) polymerase complex that contains Air1p or Air2p as potential RNA-binding subunits, as well as the putative RNA helicase Mtr4p. Comparison of native tRNAiMet with its in vitro transcribed unmodified counterpart revealed that the unmodified RNA was preferentially polyadenylated by affinity-purified Trf4 complex from yeast, as well as by complexes reconstituted from recombinant components. These results and additional experiments with other tRNA substrates suggested that the Trf4 complex can discriminate between native tRNAs and molecules that are incorrectly folded. Moreover, the polyadenylation activity of the Trf4 complex stimulated the degradation of unmodified tRNAiMet by nuclear exosome fractions in vitro. Degradation was most efficient when coupled to the polyadenylation activity of the Trf4 complex, indicating that the poly(A) tails serve as signals for the recruitment of the exosome. This polyadenylation-mediated RNA surveillance resembles the role of polyadenylation in bacterial RNA turnover.

Kinetic analysis of the RNAi enzyme complex.

Abstract: The siRNA-directed ribonucleoprotein complex, RISC, catalyzes target RNA cleavage in the RNA interference pathway. Here, we show that siRNA-programmed RISC is a classical Michaelis-Menten enzyme in the presence of ATP. In the absence of ATP, the rate of multiple rounds of catalysis is limited by release of the cleaved products from the enzyme. Kinetic analysis suggests that different regions of the siRNA play distinct roles in the cycle of target recognition, cleavage, and product release. Bases near the siRNA 5′ end disproportionately contribute to target RNA-binding energy, whereas base pairs formed by the central and 3′ regions of the siRNA provide a helical geometry required for catalysis. Finally, the position of the scissile phosphate on the target RNA seems to be determined during RISC assembly, before the siRNA encounters its RNA target.

Endogenous Viral Elements in Animal Genomes

Abstract: Integration into the nuclear genome of germ line cells can lead to vertical inheritance of retroviral genes as host alleles For other viruses, germ line integration has only rarely been documented Nonetheless, we identified endogenous viral elements (EVEs) derived from ten non-retroviral families by systematic in silico screening of animal genomes, including the first endogenous representatives of double-stranded RNA, reverse-transcribing DNA, and segmented RNA viruses, and the first endogenous DNA viruses in mammalian genomes Phylogenetic and genomic analysis of EVEs across multiple host species revealed novel information about the origin and evolution of diverse virus groups Furthermore, several of the elements identified here encode intact open reading frames or are expressed as mRNA For one element in the primate lineage, we provide statistically robust evidence for exaptation Our findings establish that genetic material derived from all known viral genome types and replication strategies can enter the animal germ line, greatly broadening the scope of paleovirological studies and indicating a more significant evolutionary role for gene flow from virus to animal genomes than has previously been recognized

Cloning and sequencing of porcine LH-hCG receptor cDNA: variants lacking transmembrane domain.

Abstract: Complementary DNA clones, encoding the LH-hCG (luteinizing hormone-human choriogonadotropic hormone) receptor were isolated by screening a lambda gt11 library with monoclonal antibodies. The primary structure of the protein was deduced from the DNA sequence analysis; the protein contains 696 amino acids with a putative signal peptide of 27 amino acids. Hydropathy analysis suggests the existence of seven transmembrane domains that show homology with the corresponding regions of other G protein-coupled receptors. Three other types of clones corresponding to shorter proteins were observed, in which the putative transmembrane domain was absent. These probably arose through alternative splicing. RNA blot analysis showed similar patterns in testis and ovary with a major RNA of 4700 nucleotides and several minor species. The messenger RNA was expressed in COS-7 cells, yielding a protein that bound hCG with the same affinity as the testicular receptor.