SummaryIn response to sublethal concentrations of antibiotics, bacteria often induce an adaptive response that can contribute to antibiotic resistance. We report the response of Bacillus subtilis to bacitracin, an inhibitor of cell wall biosynthesis found in its natural envi-

Marek's disease virus (MDV) causes a general malaise in chickens that is mostly characterized by the development of lymphoblastoid tumors in multiple organs. The use of bacterial artificial chromosomes (BACs) for cloning and manipulation of the MDV genome has facilitated characterization of specific genes and genomic regions. The development of most MDV BACs, including pRB-1B-5, derived from a very virulent MDV strain, involved replacement of the U S 2 gene with mini-F vector sequences. However, when reconstituted viruses based on pRB-1B were used in pathogenicity studies, it was discovered that contact chickens housed together with experimentally infected chickens did not contract Marek's disease (MD), indicating a lack of horizontal transmission. Staining of feather follicle epithelial cells in the skins of infected chickens showed that virus was present but was unable to be released and/or infect susceptible chickens. Restoration of U S 2 and removal of mini-F sequences within viral RB-1B did not alter this characteristic, although in vivo viremia levels were increased significantly. Sequence analyses of pRB-1B revealed that the U L 13, U L 44, and U S 6 genes encoding the U L 13 serine/threonine protein kinase, glycoprotein C (gC), and gD, respectively, harbored frameshift mutations. These mutations were repaired individually, or in combination, using two-step Red mutagenesis. Reconstituted viruses were tested for replication, MD incidence, and their abilities to horizontally spread to contact chickens. The experiments clearly showed that U S 2, U L 13, and gC in combination are essential for horizontal transmission of MDV and that none of the genes alone is able to restore this phenotype.Marek's disease virus (MDV), also known as Gallid herpesvirus 2, causes Marek's disease (MD), a lymphoproliferative disease in chickens characterized by the development of tumors in the viscera and other organs. The pathogenesis of infection with MDV can be divided into four phases (4). In the first phase, between 3 and 6 days postinfection (p.i.), the primary target cells of infection are bursa-derived (B) lymphocytes. Infection of activated CD4 ϩ thymus-derived (T) lymphocytes follows in the second phase. During the second phase, viral replication typically decreases and a latent infection is established between 5 and 10 days p.i. in activated CD4 ϩ T lymphocytes. The third phase is characterized by reactivation of MDV replication between 14 and 21 days p.i. and infection of feather follicle epithelium (FFE) cells. After the third phase, virus is shed from the chicken in dried FFE cells, and clinical MD symptoms and lymphomas may develop depending on the genetic susceptibility of the chickens and the virulence of the virus strain.The MDV genome consists of the unique short (U S ) and long (U L ) regions, flanked by the inverted repeat long (IR L ) and short (IR S ) regions, and the terminal repeat long (TR L ) and short (TR S ) regions. Through manipulation of the MDV genome using multiple approaches, specific genes or re...

pH-dependent receptor binding of specific cargo by the Erv41–Erv46 complex in Golgi compartments identifies escaped ER resident proteins that are then returned to the ER in COPI vesicles.

Coat protein complex II (COPII) vesicle formation at the endoplasmic reticulum (ER) transports nascent secretory proteins forward to the Golgi complex. To further define the machinery that packages secretory cargo and targets vesicles to Golgi membranes, we performed a comprehensive proteomic analysis of purified COPII vesicles. In addition to previously known proteins, we identified new vesicle proteins including Coy1, Sly41 and Ssp120, which were efficiently packaged into COPII vesicles for trafficking between the ER and Golgi compartments. Further characterization of the putative calcium-binding Ssp120 protein revealed a tight association with Emp47 and in emp47Δ cells Ssp120 was mislocalized and secreted. Genetic analyses demonstrated that EMP47 and SSP120 display identical synthetic positive interactions with IRE1 and synthetic negative interactions with genes involved in cell wall assembly. Our findings support a model in which the Emp47-Ssp120 complex functions in transport of plasma membrane glycoproteins through the early secretory pathway.