Rhizobium leguminosarum genes required for expression and transfer of host specific nodulation

The contributions of various nod genes from Rhizobium leguminosarum biovar viceae to host-specific nodulation have been assessed by transferring specific genes and groups of genes to R. leguminosarum bv. trifolii and testing the levels of nodulation on Pisum sativum (peas) and Vicia hirsuta. Many of the nod genes are important in determination of host-specificity; the nodE gene plays a key (but not essential) role and the efficiency of transfer of host specific nodulation increased with additional genes such that nodFE < nodFEL < nodFELMN. In addition the nodD gene was shown to play an important role in host-specific nodulation of peas and Vicia whilst other genes in the nodABCIJ gene region also appeared to be important. In a reciprocal series of experiments involving nod genes cloned from R. leguminosarum bv. trifolii it was found that the nodD gene enabled bv. viciae to nodulate Trifolium pratense (red clover) but the nodFEL gene region did not. The bv. trifolii nodD or nodFEL genes did significantly increase nodulation of Trifolium subterraneum (sub-clover) by R. leguminosarum bv. viciae. It is concluded that host specificity determinants are encoded by several different nod genes.     

Identification of the host-range DNA which allows Rhizobium leguminosarum strain TOM to nodulate cv. Afghanistan peas

Summary The special ability of Rhizobium leguminosarum strain TOM to nodulate cv. Afghanistan peas had previously been shown to be determined by the symbiotic plasmid, pRL5JI, of this strain. A region of pRL5JI, 2.0 kb in size, was found to confer the ability to nodulate cv. Afghanistan peas when transferred to strains of R. leguminosarum which normally fail to nodulate this host. This region of pRL5JI, responsible for the extension of host-range, was closely linked to, but did not include, the genes required for root hair curling. Although extensive homology has been found between the R. leguminosarum nod genes on pRL5JI and those on the normal symbiotic plasmid pRL1JI, a fragment from the 2.0 kb region involved in nodulation of cv. Afghanistan has been identified, which was not homologous to DNA in strains which do not nodulate cv. Afghanistan.     

Molecular cloning and genetic organization of C4-dicarboxylate transport genes from Rhizobium leguminosarum.

Cosmids containing C4-dicarboxylate transport (dct) genes were identified from a gene bank of Rhizobium leguminosarum DNA made in the broad-host-range vector pLAFR1 by their ability to complement R. trifolii dct mutants. The dct genes were further characterized by subcloning, restriction site mapping, and transposon Tn5 and Tn7 mutageneses. Three dct loci were identified within a 5.5-kilobase region of DNA, in the order dctA-dctB-dctC. The results suggested that dctA encoded a structural component necessary for C4-dicarboxylate transport, whereas dctB and dctC encoded positive regulatory elements, and that dctA was transcribed divergently from dctB and dctC. Expression of dctA and dctC was obtained from vector promoters in some pLAFR1- and pSUP106-based plasmids.     

Cloned nodulation genes of Rhizobium leguminosarum determine host-range specificity

Summary Three nodulation-deficient (nod) mutants of Rhizobium leguminosarum were isolated following insertion of the transposon Tn5 into pRL1JI, the R. leguminosarum plasmid known to carry the nodulation genes. DNA adjacent to the nod: Tn5 alleles was subcloned and used to probe a cosmid clone bank containing DNA from a Rhizobium strain carrying pRL1JI. Two cosmid clones which showed homology with the probe contained about 10 kb of DNA in common. The R. leguminosarum host-range determinants were found to be present within this 10 kb common region since either of the cosmid clones could enable a cured R. phaseoli strain to nodulate peas instead of Phaseolus beans, its normal host. Electron microscopy of nodules induced by Rhizobium strains cured of their normal symbiotic plasmid but containing either of the two cosmid clones showed bacteroid-forms surrounded by a peri-bacteroid membrane, indicating that normal infection had occurred. Thus it is clear that this 10 kb region of nodDNA carries the genes that determine host range and that relatively few bacterial genes may be involved in nodule and bacteroid development.     

Mutations in the uncE gene affecting assembly of the c-subunit of the adenosine triphosphatase of Escherichia coli.

The amino acid substitutions in the mutant c-subunits of Escherichia coli F1F0-ATPase coded for by the uncE429, uncE408 and uncE463 alleles affect the incorporation of these proteins into the cell membrane. The DNA sequence of the uncE429 allele differed from normal in that a G leads to A base change occurred at nucleotide 68 of the uncE gene, resulting in glycine being replaced by aspartic acid at position 23 in the c-subunit. The uncE408 and uncE463 mutant DNA sequences were identical and differed from normal in that a C leads to T base change occurred at nucleotide 91 of the uncE gene, resulting in leucine being replaced by phenylalanine at position 31 in the c-subunit. An increased gene dosage of the uncE408 or uncE463 alleles resulted in the incorporation into the membranes of the mutant c-subunits. The results are discussed in terms of the 'Helical Hairpin Hypothesis' of Engelman & Steitz [(1981) Cell 23,411-422].     

Clinical Trial of Lincomycin Hydrochloride in Reiter's Disease

A double-blind trial comparing lincomycin hydrochloride (Mycivin) and placebo in 22 patients with Reiter''s disease showed no significant difference in clinical or laboratory findings between the two groups. It is concluded that lincomycin hydrochloride is no more effective than placebo in the treatment of Reiter''s disease.     

A comparative study of the glomerular peripolar cell and the renin-secreting cell in twelve mammalian species

The peripolar cell is a glomerular epithelial cell situated within Bowman's capsule at its vascular pole. It is believed to be a secretory cell which forms part of the juxtaglomerular apparatus. Scanning electron microscopy was used to perform a comparative study of the morphology and number of peripolar cells in twelve mammalian species. The number of renin-secreting cells in kidney sections stained by renin antibodies and immunocytochemistry was counted. There was a marked inter-species variation in the number, size and appearance of peripolar cells. They were largest and most abundant in sheep and goat and fewest in dog, cow and human. There was no correlation between the numbers of peripolar cells and renin-secreting cells. This does not support the view that the peripolar cell is part of the juxtaglomerular apparatus.