A possible role for acetylated intermediates in diaminopimelate and tabtoxinine-beta-lactam biosynthesis in Pseudomonas syringae pv. tabaci BR2.024.
The deduced product of an open reading frame (ORF3) located in the tabtoxinine-beta-lactam (T beta L) biosynthetic region of Pseudomonas syringae pv. tabaci BR2.024 (BR2.024) has significant sequence homology to the dapD products of other bacteria. dapD encodes L-2,3,4,5-tetrahydrodipicolinate succinyl coenzyme A succinyltransferase (THDPA-ST), an enzyme in the diaminopimelate (DAP) and lysine biosynthetic pathway. Complementation studies, in vitro transcription-translation experiments, and enzymatic assays indicated that ORF3 encodes a product with THDPA-ST activity in Escherichia coli dapD mutant beta 274. However, a BR2.024 mutant with an insert in ORF3 was prototrophic, and only basal THDPA-ST activity was detected in extracts of both parent and mutant. This finding suggested that ORF3 was not required for DAP biosynthesis and that it did not encode a product with THDPA-ST activity. The results of enzymatic studies, indicating that BR2.024 uses acetylated intermediates for DAP biosynthesis, are consistent with the hypothesis that BR2.024 does not need THDPA-ST for DAP biosynthesis. The ORF3 mutant produced reduced levels of tabtoxin, indicating that ORF3 may have a role in T beta L biosynthesis. We have named the gene tabB and have proposed a possible function for the gene product.
Liu
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Department of Crop Sciences, University of Illinois, Urbana-Champaign 61801, USA.
Shaw
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PD
D000107:Acetylation; D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism*; D000217:Acyltransferases / Q000235:genetics; D000595:Amino Acid Sequence; D001384:Azetidines / Q000378:metabolism*; D001426:Bacterial Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D003960:Diaminopimelic Acid / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D005816:Genetic Complementation Test; D008239:Lysine / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011549:Pseudomonas / Q000378:metabolism*; D015183:Restriction Mapping; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D047090:beta-Lactams / Q000378:metabolism*
D001384:Azetidines; D001426:Bacterial Proteins; D047090:beta-Lactams; D003960:Diaminopimelic Acid; C051368:tabtoxinine beta-lactam; D000217:Acyltransferases; D000123:Acetyltransferases; C108307:TabB protein, Pseudomonas syringae; C040777:succinyl-CoA-tetrahydrodipicolinate N-succinyltransferase; D008239:Lysine