Meeting Report for Mobile DNA 2010

An international conference on mobile DNA was held 24-28 April 2010 in Montreal, Canada. Sponsored by the American Society for Microbiology, the conference's goal was to bring together researchers from around the world who study transposition in diverse organisms using multiple experimental approaches. The meeting drew over 190 attendees and most contributed through poster presentations, invited talks and short talks selected from poster abstracts. The talks were organized into eight scientific sessions, which ranged in topic from the evolutionary dynamics of mobile genetic elements to transposition reaction mechanisms. Here we present highlights from the platform sessions with a focus on talks presented by the invited speakers

Diploma Privilege and the Constitution

The COVID-19 pandemic and resulting shutdowns are affecting every aspect of society. The legal profession and the justice system have been profoundly disrupted at precisely the time when there is an unprecedented need for legal services to deal with a host of legal issues generated by the pandemic, including disaster relief, health law, insurance, labor law, criminal justice, domestic violence, and civil rights. The need for lawyers to address these issues is great but the prospect of licensing new lawyers is challenging due to the serious health consequences of administering the bar examination during the pandemic. State Supreme Courts are actively considering alternative paths to licensure. One such alternative is the diploma privilege, a path to licensure currently used only in Wisconsin. Wisconsin\u27s privilege, limited to graduates of its two in-state schools, has triggered constitutional challenges never fully resolved by the lower courts. As states consider emergency diploma privileges to address the pandemic, they will face these unresolved constitutional issues. This Article explores those constitutional challenges and concludes that a diploma privilege limited to graduates of in-state schools raises serious Dormant Commerce Clause questions that will require the state to tie the privilege to the particular competencies in-state students develop and avenues they have to demonstrate those competencies to the state\u27s practicing bar over three years. Meeting that standard will be particularly difficult if a state adopts an in-state privilege on an emergency basis. States should consider other options, including privileges that do not prefer in-state schools. The analysis is important both for states considering emergency measures and for those that might restructure their licensing after the pandemic

The Bar Exam and the COVID-19 Pandemic: The Need for Immediate Action

The novel coronavirus COVID-19 has profoundly disrupted life in the United States. Among other challenges, jurisdictions are unlikely to be able to administer the July 2020 bar exam in the usual manner. It is essential, however, to continue licensing new lawyers. Those lawyers are necessary to meet current needs in the legal system. Equally important, the demand for legal services will skyrocket during and after this pandemic. We cannot close doors to the profession at a time when client demand will reach an all-time high.In this brief policy paper, we outline six licensing options for jurisdictions to consider for the Class of 2020. Circumstances will vary from jurisdiction to jurisdiction, but we hope that these options will help courts and regulators make this complex decision. These are unprecedented times: We must work together to ensure we do not leave the talented members of Class of 2020 on the sidelines when we need every qualified professional on the field to keep our justice system moving

Retrosequence formation restructures the yeast genome

Retrosequences generated by reverse transcription of mRNA transcripts have a substantial influence on gene expression patterns, generation of novel gene functions, and genome organization. The Ty1 retrotransposon is a major source of RT activity in the yeast, Saccharomyces cerevisiae, and Ty1 retromobility is greatly elevated in strains lacking telomerase. We report that Ty1-dependent formation of retrosequences derived from single-copy gene transcripts is progressively elevated as yeast cells senesce in the absence of telomerase. Retrosequences are frequently fused to Ty1 sequences, and occasionally to sequences from other mRNA transcripts, forming chimeric pseudogenes. Efficient retrosequence formation requires the homologous recombination gene RAD52. Selection for retrosequence formation is correlated with a high frequency of chromosome rearrangements in telomerase-negative yeast. Ty1-associated retrosequences were present at the breakpoint junctions of four chromosomes analyzed in detail. Our results support a role for reverse transcripts in promoting chromosome rearrangements

Hos2 and Set3 Promote Integration of Ty1 Retrotransposons at tRNA Genes in Saccharomyces cerevisiae

The yeast LTR retrotransposon Ty1 integrates preferentially into regions upstream of tRNA genes. The chromatin structure of transcriptionally active tRNA genes is known to be important for Ty1 integration, but specific chromatin factors that enhance integration at tRNA genes have not been identified. Here we report that the histone deacetylase, Hos2, and the Trithorax-group protein, Set3, both components of the Set3 complex (Set3C), enhance transposition of chromosomal Ty1 elements by promoting integration into the upstream region of tRNA genes. Deletion of HOS2 or SET3 reduced the mobility of a chromosomal Ty1his3AI element about sevenfold. Despite the fact that Ty1his3AI RNA, total Ty1 RNA, and total Ty1 cDNA levels were not reduced in hos2Δ or set3Δ mutants, transposition of endogenous Ty1 elements into the upstream regions of tRNA(Gly) genes was substantially decreased. Furthermore, when equivalent numbers of Ty1HIS3 mobility events launched from a pGAL1:Ty1his3AI plasmid were analyzed, only one-quarter to one-half as many were found upstream of tRNA(Gly) genes in a hos2Δ or set3Δ mutant than in a wild-type strain. Chromatin immunoprecipitation analysis revealed that Hos2 is physically associated with tRNA genes. Taken together, our results support the hypothesis that Hos2 and Set3 function at tRNA genes to promote Ty1 integration

Nuclear expression of a group II intron is consistent with spliceosomal intron ancestry

Group II introns are self-splicing RNAs found in eubacteria, archaea, and eukaryotic organelles. They are mechanistically similar to the metazoan nuclear spliceosomal introns; therefore, group II introns have been invoked as the progenitors of the eukaryotic pre-mRNA introns. However, the ability of group II introns to function outside of the bacteria-derived organelles is debatable, since they are not found in the nuclear genomes of eukaryotes. Here, we show that the Lactococcus lactis Ll.LtrB group II intron splices accurately and efficiently from different pre-mRNAs in a eukaryote, Saccharomyces cerevisiae. However, a pre-mRNA harboring a group II intron is spliced predominantly in the cytoplasm and is subject to nonsense-mediated mRNA decay (NMD), and the mature mRNA from which the group II intron is spliced is poorly translated. In contrast, a pre-mRNA bearing the Tetrahymena group I intron or the yeast spliceosomal ACT1 intron at the same location is not subject to NMD, and the mature mRNA is translated efficiently. Thus, a group II intron can splice from a nuclear transcript, but RNA instability and translation defects would have favored intron loss or evolution into protein-dependent spliceosomal introns, consistent with the bacterial group II intron ancestry hypothesis

Co-translational Localization of an LTR-Retrotransposon RNA to the Endoplasmic Reticulum Nucleates Virus-Like Particle Assembly Sites

<div><p>The transcript of retrovirus-like transposons functions as an mRNA for synthesis of capsid and replication proteins and as the genomic RNA of virus-like particles (VLPs), wherein the genome is replicated. Retrotransposon RNA and proteins coalesce in a cytoplasmic focus, or retrosome, to initiate VLP assembly, but it is not known how the retrosome is nucleated. We determined how the RNA and Gag protein of the <i>Saccharomyces cerevisiae</i> Ty1 retrotransposon are directed to the retrosome. We found that Ty1 RNA is translated in association with signal recognition particle (SRP), a universally conserved chaperone that binds specific ribosome-nascent chain (RNC) complexes and targets the nascent peptide to the endoplasmic reticulum (ER). Gag is translocated to the ER lumen; yet, it is also found in the cytoplasm, associated with SRP-RNC complexes. In the absence of ER translocation, Gag is synthesized but rapidly degraded, and Ty1 RNA does not coalesce in retrosomes. These findings suggest that Gag adopts a stable conformation in the ER lumen, is retrotranslocated to the cytoplasm, binds to Ty1 RNA on SRP-RNC complexes and multimerizes to nucleate retrosomes. Consistent with this model, we show that slowing the rate of co-translational ER translocation by limiting SRP increases the prevalence of retrosomes, while suppressing the translocation defect of <i>srp</i> hypomorphs by slowing translational elongation rapidly decreases retrosome formation. Thus, retrosomes are dynamic foci of Ty1 RNA-RNC complexes whose formation is modulated by the rate of co-translational ER translocation. Together, these findings suggest that translating Ty1 mRNA and the genomic RNA of VLPs originate in a single pool and moreover, that co-translational localization of Ty1 RNA nucleates the presumptive VLP assembly site. The separation of nascent Gag from its RNA template by transit through the ER allows Gag to bind translating Ty1 RNA without displaying a <i>cis</i>-preference for its encoding RNA.</p></div