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Differential and Cross-Transcriptional Control of Duplicated Genes Encoding Alternative Sigma Factors in Streptomyces ambofaciens.
Virginie Roth, 2004.The duplicated hasR and hasL genes of Streptomyces ambofaciens encode alternative sigma factors (named

^B_R and

^B_L) belonging to the

^B general stress response family in Bacillus subtilis . The duplication appears to be the result of a recent event that occurred specifically in S . ambofaciens . The two genes are 98% identical, and their deduced protein products exhibit 97% identity at the amino acid level . In contrast with the coding sequences, their genetic environments and their transcriptional control are strongly divergent . While hasL is monocistronic, hasR is arranged in a polycistronic unit with two upstream open reading frames, arsR and prsR, that encode putative anti-anti-

and anti-

factors, respectively . Transcription of each has gene is initiated from two promoters . In each case, one promoter was shown to be developmentally controlled and to be similar to those recognized by the B . subtilis general stress response sigma factor

^B . Expression from this type of promoter for each of the has genes dramatically increases during the course of growth in liquid or on solid media and following oxidative and osmotic stresses . Reverse transcription-PCR measurements indicate that hasR is 100 times more strongly expressed than hasL from the

^B-like promoter . Transcription from the second promoter of each gene (located upstream of arsR in the case of the hasR locus) appears to be constitutive and weak . Quantitative transcriptional analysis in single and double has mutant strains revealed that

^B_R and

^B_L direct their own transcription as well as that of their duplicates . Only a slight sensitivity in response to oxidative conditions could be assigned to either single or double mutants, revealing the probable redundancy of the

factors implied in stress response in Streptomyces .

Natural Polymorphism of Cytomegalovirus DNA Polymerase Lies in Two Nonconserved Regions Located between Domains Delta-C and II and between Domains III and I.
Anne-Marie Fillet, 2004.We described the natural polymorphism of cytomegalovirus DNA polymerase in 42 unrelated isolates susceptible to ganciclovir, foscarnet, and cidofovir . All variations, including an eight-amino-acid deletion, were located between domains delta-C and II and between domains III and I, suggesting that these specific residues are not involved in enzymatic functions .

Rhizobium etli and Rhizobium gallicum Nodulate Common Bean (Phaseolus vulgaris) in a Traditionally Managed Milpa Plot in Mexico: Population Genetics and Biogeographic Implications.
Claudia Silva, 2003.The stability of the genetic structure of rhizobial populations nodulating Phaseolus vulgaris cultivated in a traditionally managed milpa plot in Mexico was studied over three consecutive years . The set of molecular markers analyzed (including partial rrs, glnII, nifH, and nodB sequences), along with host range experiments, placed the isolates examined in Rhizobium etli bv . phaseoli and Rhizobium gallicum bv . gallicum . Cluster analysis of multilocus enzyme electrophoresis and plasmid profile data separated the two species and identified numerically dominant clones within each of them . Population genetic analyses showed that there was high genetic differentiation between the two species and that there was low intrapopulation differentiation of the species over the 3 years . The results of linkage disequilibrium analyses are consistent with an epidemic genetic structure for both species, with frequent genetic exchange taking place within conspecific populations but not between the R . etli and R . gallicum populations . A subsample of isolates was selected and used for 16S ribosomal DNA PCR-restriction fragment length polymorphism analysis, nifH copy number determination, and host range experiments . Plasmid profiles and nifH hybridization patterns also revealed the occurrence of lateral plasmid transfer among distinct multilocus genotypes within species but not between species . Both species were recovered from nodules of the same plants, indicating that mechanisms other than host, spatial, or temporal isolation may account for the genetic barrier between the species . The biogeographic implications of finding an R . gallicum bv . gallicum population nodulating common bean in America are discussed .

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Last modified: May 25, 2005