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#Ara operon

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Gene regulation in Prokaryotes

Ara operon structural genes are

Arabinose structural genes are organized as contiguous araBAD cluster transcribed as single polycistronic messenger from PBAD promoter under dual control. araB encodes ribulokinase enzyme phosphorylating L-ribulose using ATP producing ribulose-5-phosphate; araA encodes L-arabinose isomerase converting L-arabinose aldose to L-ribulose ketose; araD encodes L-ribulose-5-phosphate 4-epimerase generating D-xylulose-5-phosphate which enters pentose phosphate pathway for energy and biosynthesis. Together three enzymes divert abundant plant-derived pentose sugar into central carbon metabolism. araC regulatory gene transcribed divergently from same intergenic control region forms separate transcription unit with autoregulated PC promoter.

Ref: PMC Transcriptional Control L-Arabinose Operon – structural genes araB A D metabolize arabinose via PBAD promoter.

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Gene regulation in Prokaryotes

Ara operon is an example of

Arabinose operon exemplifies inducible catabolic system controlling pentose sugar utilization in Escherichia coli. Genes remain transcriptionally silent without substrate because apo-AraC regulator forms DNA loop repressing PBAD promoter activity. Presence of L-arabinose sugar converts regulatory protein into transcriptional activator capable of recruiting polymerase. Operon therefore defaults off state, switched on only upon metabolite accumulation, similar regulatory logic to lac induction by allolactose inducer and distinct from trp repressible anabolic logic where end product shuts off. Additional control by glucose through CAP-cAMP complex ensures carbon source hierarchy maximizing growth efficiency while retaining ability to metabolize arabinose when preferred sugars depleted.

Ref: Wikipedia L-arabinose operon – araBAD inducible operon regulated by AraC and CAP-cAMP catabolite control.

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