A mutualistic association between a fungal endophyte and a tropical panic grass allows both organisms to grow at high soil temperatures. We characterized a virus from this fungus that is involved in the mutualistic interaction. Fungal isolates cured of the virus are unable to confer heat tolerance, but heat tolerance is restored after the virus is reintroduced. The virus-infected fungus confers heat tolerance not only to its native monocot host but also to a eudicot host, which suggests that the underlying mechanism involves pathways conserved between these two groups of plants.
Bacillus subtilis contains multiple forms of RNA pol,ymerase holoenzyme, distinguished by the presence of different specificiy determinants known as (r factors.. The au factor was initially purified as a unique transcriptional activity in vegetatively growing B. subtilis cells. Purification of the a8 protein has allowed tryptic peptides to be prepared and sequenced. The sequence of one tryptic peptide fragment was used to prepare an oligonucleotide probe specific for the a8 -structural gene, and the gene was isolated from a B. subtilis subgenomic library. The complete nucleotide sequence of the a8 gene was determined, and the cloned 28 (F gene was used to construct a mutant strain which does not express the ('8 protein. This strain also failed to synthesize flageilin protein and grew as long filaments. The predicted (28 gene product is a 254-amino-acid polypeptide with a calculated molecular weight of 29,500. The d8 protein sequence was similar to that of other sequenced 'r factors and to theflbB gene product of Escherichia coli. Since theflbB gene product is a positive regulator of flagellar synthesis in E. coli, it is likely that cr8 functions to regulate flagellar synthesis in B. subtilis.Bacterial RNA polymerase is a multisubunit enzyme central to the process of gene expression. Although the catalytic activity resides in the core subunits of the enzyme, the promoter specificity of a particular holoenzyme is determined by the nature of the associated a factor (31). The majority of cellular transcription is dependent on the primary r factor, which exhibits a conserved promoter recognition specificity throughout the eubacteria (43). Many bacterial species also contain alternative a factors that are specific for transcription of distinct regulons of coordinately regulated genes. These alternative a factors normally recognize promoter sequences that are differett from those recognized by the primary cr factor. Examhples of alternative of factors in the enteric bacteria include a32 (15), specific for the transcription of heat shock genes, and (94 (19, 20), specific for transcription of fnitrogen-regulated genes. For Bacillus subtilis, at least six alternative factors have been described (26,31).In B. subtilis, alterations in cellular transcription, mediated at least in part by alternative cr factors, effect the precise temporal changes in gene expression necessary for endospore formation (26). The products of the spoOH (U30) and spoIIGB (r29) genes are sporulation-specific cr factors that have been characterized both genetically and biochemically (6,22,24,26,40,41). In addition, the spoIIAC gene product is homologous to other sequenced a factors (9) and may also function as a cf factor. The cr3 and a98 factors are found in vegetatively growing cells and are dispensable for sporulation, since disruption of these genes does not impair sporulation (3, 8; see below). To define the biological function of the B. subtilis ur28 factor, we have begun a genetic and structural analysis of the Cr28 structural gene (sigD) bas...
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