PLANT PHYSIOLOGY , Vol 104, Issue 2 461-466, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Synechocystis PCC 6803 Contains a Single Gene for the [beta] Subunit of Tryptophan Synthase with Strong Homology to the trpB Genes of Arabidopsis and Maize (Zea mays L.)
G. P. Zhao, R. L. Somerville and P. R. Chitnis
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907-1153 (G.-P.Z., R.L.S.)
We report the sequence of the trpB gene of the cyanobacterium Synechocystis
sp. PCC 6803. This gene was cloned from a plasmid library by functional
complementation of a trpB mutant of Escherichia coli K-12. Among the known
trpB sequences, the Synechocystis gene bears the greatest homology to the
duplicated trpB genes of Arabidopsis thaliana and Zea mays. Southern and
northern blotting analyses suggest that Synechocystis contains only a
single trpB gene. In contrast to all other prokaryotes, Synechocystis has a
trpB gene that is monocistronic. Attempts to construct a trpB null mutant
of Synechocystis by standard techniques were unsuccessful, suggesting that
this organism is unable to concentrate tryptophan from the external medium.