Biomedical subjects

G Selvaraj

Publications and source records attributed to G Selvaraj.

22 records · Page 2Linked to original sources

PubMed1984

Transposon Tn5 specifies streptomycin resistance in Rhizobium spp.

Transposon Tn5 conferred streptomycin resistance on different strains of Rhizobium meliloti, Rhizobium leguminosarum, and Rhizobium trifolii but not on Escherichia coli. A gene (str) specifying this phenotype has been identified and localized on the physical and genetic map of Tn5. It is transcribed from the promoter of neo, the gene that encodes neomycin phosphotransferase. The str gene is downstream from neo in a single transcriptional unit, as revealed by molecular cloning of different segments of Tn5 and by cloning of the neo-str region of Tn5 downstream from a lac promoter. Fusion of the SalI-generated rightward segment of Tn5 (devoid of neo) to a part of a tetracycline resistance gene, tet, in a plasmid or downstream from a lac promoter in a plasmid resulted in significant levels of streptomycin resistance in an R. meliloti host, suggesting that the str gene product can function independent of neomycin phosphotransferase. A natural isolate of R. meliloti that does not express Tn5-associated streptomycin resistance has been identified. We have used the str of Tn5 as a genetic marker in Rhizobium spp.

DNA Transposable Elements↗

PubMed1983

Suicide plasmid vehicles for insertion mutagenesis in Rhizobium meliloti and related bacteria.

We describe the construction and use of a set of plasmid vectors of the transposons Tn1, Tn5, and Tn9 that are suicidal in Rhizobium species and therefore suitable for mutagenesis with these three transposons. The vectors are composed of the p15A replicon which functions in Escherichia coli but not in Rhizobium species and a region encoding the N type of bacterial conjugation system which is very efficient in matings between E. coli and Rhizobium species. The usefulness of the vectors has been most extensively assessed in Rhizobium meliloti. It is likely that they will be useful for mutagenesis and genome manipulation in other bacteria as well.

Conjugation, Genetic↗

PubMed1981

Genetic transformation of Rhizobium meliloti by plasmid DNA.

A procedure for the genetic transformation of Rhizobium meliloti by plasmid DNA is described. It is an adaptation of a procedure used originally for Escherichia coli and later for Agrobacterium tumefaciens. Depending on the R. meliloti isolate used as the recipient, the efficiency of transformation was in the range of 7 x 10(1) to 3.7 x 10(3) per microgram of plasmid pRK248 DNA and 10(-6) to 10(-9) per viable cell. A number of different naturally occurring strains could be transformed. Plasmids related to pRK248 and varying in size from 9.6 to 56 kb could be used, suggesting that the procedure will be useful for molecular cloning of genes in R. meliloti.

Cloning, Molecular↗

PubMed1980

A dnaB analog function specified by bacteriophage P7 and its comparison to the similar function specified by bacteriophage P1.

Evidence is presented that bacteriophage P7 specifies an analog of the E. coli DNA replication protein, dnaB. As in the related bacteriophage P1 (D'Ari et al., 1975; Ogawa, 1975), in lysogens of P7, the production of the analog protein is repressed and constitutive mutants could be isolated. Such constitutive mutants could suppress efficiently the thermosensitivity of several dnaB(ts) mutations and also rescue a strain carrying a dnaB amber mutation. While neither P7 nor the mutant P1bacban (defective in the structural gene ban) could suppress dnaB(ts) mutations efficiently, recombinants between these two phages could do so, indicating the presence of a functional dnaB analog gene (called sdb) on P7. In a dnaB amber strain suppressed by the presence of the constitutive mutant P7csb, bacteriophage lambda failed to replicate which is a further similarity between P7 and P1. P7csb mutants or P7-P1bacban recombinants were found to be less thermoresistant than P1bac1 suggesting that the P7-specified dnaB analog protein or its production is relatively less tolerant of temperatures above 37 degrees C.

Coliphages↗