Cytoplasmic mRNA localization provides a means of generating cell asymmetry and segregating protein activity. Previous studies have identified two mRNAs that localize to the bud tips of the yeast Saccharomyces cerevisiae. To identify additional localized mRNAs, we immunoprecipitated the RNA transport components She2p, She3p, and Myo4p and performed DNA microarray analysis of their associated RNAs. A secondary screen, using a GFP-tagged RNA reporter assay, identified 22 mRNAs that are localized to bud tips. These messages encode a wide variety of proteins, including several involved in stress responses and cell wall maintenance. Many of these proteins are asymmetrically localized to buds. However, asymmetric localization also occurs in the absence of RNA transport, suggesting the existence of redundant protein localization mechanisms. In contrast to findings in metazoans, the untranslated regions are dispensable for mRNA localization in yeast. This study reveals an unanticipated widespread use of RNA transport in budding yeast.

In Saccharomyces cerevisiae, telomeric DNA is protected by a nonnucleosomal protein complex, tethered by the protein Rap1. Rif and Sir proteins, which interact with Rap1p, are thought to have further interactions with conventional nucleosomic chromatin to create a repressive structure that protects the chromosome end. We showed by microarray analysis that Rif1p association with the chromosome ends extends to subtelomeric regions many kilobases internal to the terminal telomeric repeats and correlates strongly with the previously determined genomic footprints of Rap1p and the Sir2-4 proteins in these regions. Although the end-protection function of telomeres is essential for genomic stability, telomeric DNA must also be copied by the conventional DNA replication machinery and replenished by telomerase, suggesting that transient remodeling of the telomeric chromatin might result in distinct protein complexes at different stages of the cell cycle. Using chromatin immunoprecipitation, we monitored the association of Rap1p, Rif1p, Rif2p, and the protein component of telomerase, Est2p, with telomeric DNA through the cell cycle. We provide evidence for dynamic remodeling of these components at telomeres. INTRODUCTIONTelomeres are nonnucleosomal protein-DNA complexes that prevent uncontrolled fusion, degradation, recombination, and elongation of chromosome ends (Muller, 1938;McClintock, 1941;Wright et al., 1992;Sandell and Zakian, 1993;Hande et al., 1999;Smith and Blackburn, 1999;Hackett et al., 2001). In Saccharomyces cerevisiae, terminal telomeric DNA is composed of ϳ350 base pairs of short, degenerate TG 1-3 repeats. One telomeric strand is polymerized by telomerase (Cohn and Blackburn, 1995) and forms an S-phasespecific TG 1-3 overhang (Wellinger et al., 1993(Wellinger et al., , 1996. The conventional DNA polymerase machinery is thought to synthesize the complementary C 1-3 A strand. Duplex telomeric DNA repeats are bound by the sequence-specific binding protein Rap1p, which recruits proteins Rif1p and Rif2p as well as Sir3p and Sir4p via its C-terminal domain (Moretti et al., 1994;Moazed and Johnson, 1996;Moretti and Shore, 2001).Telomeric regions in yeast also contain subtelomeric X-elements, which have only moderate homology to each other and are present at all chromosome ends, and the highly homologous YЈ elements located distal to the X elements (Chan and Tye, 1983) on about half of all chromosome ends. YЈ elements fall into 5.2-and 6.7-kb size classes (Louis and Haber, 1990;Louis and Haber, 1992), encode a helicase (Yamada et al., 1998), and are bounded by short (Ͻ150-base pair) tracts of internal telomeric TG 1-3 sequence DNA. Because YЈ elements often occur in tandem arrays of two to four repeats, these TG 1-3 tracts are found internal to the chromosome ends at distances depending upon the size class and number of YЈ elements present.The Rap1p, Ku, and Sir2-4 proteins are cross-linkable to DNA as far in as 3-15 kb from the chromosome end, consistent with their simultaneous binding to TG [1][2][3] repeat DNA ...

Background There is urgent need to understand the dynamics and risk factors driving ongoing SARS-CoV-2 transmission during shelter-in-place mandates. Methods We offered SARS-CoV-2 reverse transcription-PCR and antibody (Abbott ARCHITECT IgG) testing, regardless of symptoms, to all residents (≥4 years) and workers in a San Francisco census tract (population: 5,174) at outdoor, community-mobilized events over four days. We estimated SARS-CoV-2 point prevalence (PCR-positive) and cumulative incidence (antibody or PCR-positive) in the census tract and evaluated risk factors for recent (PCR-positive/antibody-negative) versus prior infection (antibody-positive/PCR-negative). SARS-CoV-2 genome recovery and phylogenetics were used to measure viral strain diversity, establish viral lineages present, and estimate number of introductions. Results We tested 3,953 persons: 40% Latinx; 41% White; 9% Asian/Pacific Islander; and 2% Black. Overall, 2.1% (83/3,871) tested PCR-positive: 95% were Latinx and 52% asymptomatic when tested. 1.7% of census tract residents and 6.0% of workers (non-census tract residents) were PCR-positive. Among 2,598 tract residents, estimated point prevalence of PCR-positives was 2.3% (95%CI: 1.2-3.8%): 3.9% (95%CI: 2.0-6.4%) among Latinx vs. 0.2% (95%CI: 0.0-0.4%) among non-Latinx persons. Estimated cumulative incidence among residents was 6.1% (95%CI: 4.0-8.6%). Prior infections were 67% Latinx, 16% White, and 17% other ethnicities. Among recent infections, 96% were Latinx. Risk factors for recent infection were Latinx ethnicity, inability to shelter-in-place and maintain income, frontline service work, unemployment, and household income &$50,000/year. Five SARS-CoV-2 phylogenetic lineages were detected. Conclusion SARS-CoV-2 infections from diverse lineages continued circulating among low-income, Latinx persons unable to work from home and maintain income during San Francisco’s shelter-in-place ordinance.