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psi, a plasmid-linked Rhizobium phaseoli gene that inhibits exopolysaccharide production and which is required for symbiotic nitrogen fixation

โœ Scribed by Borthakur, D. ;Downie, J. A. ;Johnston, A. W. B. ;Lamb, J. W.

Publisher
Springer
Year
1985
Tongue
English
Weight
513 KB
Volume
200
Category
Article
ISSN
0026-8925

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โœฆ Synopsis

A strain of R. phaseoIi cured of its symbiotic plasmid, pRP2JI, retained the ability to make exopolysaccharide (EPS). However, a region of pRP2JI, when cloned at an increased copy number in wide host-range vectors and transferred to this and other strains of Rhizobium, inhibited EPS synthesis. The gene responsible was termed psi (polysaccharide inhibition) and was located in a region of the symbiotic plasmid close to nodulation and nitrogen fixation genes, psi is important in the symbiosis since a wild-type strain containing psi cloned on a multicopy plasmid failed to form Phaseolus nodules, and mutant strains containingpsi: :Tn5 mutations failed to fix nitrogen in Phaseolus nodules. It is proposed that the function of psi may be to repress in the bacteroid the expression of genes such as those for EPS synthesis which are normally expressed in free-living culture.

๐Ÿ“œ SIMILAR VOLUMES

Sequence of psi, a gene on the symbiotic
Sequence of psi, a gene on the symbiotic plasmid of Rhizobium phaseoli which inhibits exopolysaccharide synthesis and nodulation and demonstration that its transcription is inhibited by psr, another gene on the symbiotic plasmid
โœ Borthakur, D. ;Johnston, A. W. B. ๐Ÿ“‚ Article ๐Ÿ“… 1987 ๐Ÿ› Springer ๐ŸŒ English โš– 626 KB

A gene termed psi (polysaccharide inhibition), located close to the nodulation genes of the Rhizobium phaseoli symbiotic plasmid pRP2JI inhibited exopolysaccharide synthesis (EPS) and nodulation ability (Nod) in Rhizobium when it was cloned in a multicopy plasmid. The sequence of psi showed that it