RESUMO
Some mutants of Agrobacterium radiobacter, defective in exopolysaccharide synthesis, were phenotypically complemented by two different regions of cloned chromosomal DNA. One of these had been shown to contain a gene termed ros, a novel class of transcriptional regulator. The other contains a gene termed exoY which encodes a glycosyltransferase that is involved in one of the early steps in exopolysaccharide synthesis. Mutations in ros reduced the expression of exoY and a model to account for the complementation of certain exo alleles by both ros and exoY is presented. TnphoA insertions into exoY which expressed alkaline phosphatase activity were isolated and mapped, confirming the membrane location of the exoY gene product. Some of these mutations were dominant, causing merodiploids to be non-mucoid. exoY is linked to two genes, one encoding an omega-aminotransferase and the other encoding an aldehyde dehydrogenase.
Assuntos
Proteínas de Bactérias , Proteínas de Ligação a DNA/genética , Regulação Bacteriana da Expressão Gênica , Glicosiltransferases/genética , Proteínas Repressoras/genética , Rhizobium/genética , Membro 1 da Subfamília D de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/genética , Alelos , Sequência de Aminoácidos , Proteínas de Transporte de Ânions , Proteínas de Transporte/genética , Mapeamento Cromossômico , Clonagem Molecular , Teste de Complementação Genética , Proteínas de Membrana/genética , Dados de Sequência Molecular , Mutagênese Insercional , Plasmídeos , Polissacarídeos/metabolismo , Transcrição GênicaRESUMO
Four exo mutants of Agrobacterium radiobacter, defective in the synthesis of acidic exopolysaccharide were complemented by a gene from that species, which is similar to the transcriptional regulator, ros, of A. tumefaciens. It was confirmed that this A. radiobacter gene, which we term rosAR, like ros, repressed its own transcription as well as that of virC and virD, two loci involved in tumorigenesis. The sequence of RosAR suggested that it might bind to a transition metal and its repressor abilities were shown to require Fe in the medium; repression was also enhanced with increasing levels of glucose. Certain rosAR mutants, in which its 3' end was removed were dominant; i.e., when plasmids containing such mutant forms of the gene were introduced into wild-type A. radiobacter, the transconjugants were nonmucoid. Such effects were also seen in a wide range of bacteria, including Escherichia coli and Xanthomonas. Several mutants that were complementd by rosAR also accumulated protoporphyrin, suggesting a defect in haem synthesis.
