Gene Ontology annotation through association of InterPro records with GO terms
Automatic assignment of GO terms using logical inference, based on on inter-ontology links
Electronic Gene Ontology annotations created by ARBA machine learning models
Combined Automated Annotation using Multiple IEA Methods
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Supplied both the precise GO:0046905 row grounded in RHEA:34475 and EC 2.5.1.32, which is accepted, and the over-general GO:0016765 transferase row, which is modified to the specific activity.
Elucidation of the Erwinia uredovora carotenoid biosynthetic pathway by functional analysis of gene products expressed in Escherichia coli.
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Cloned the six-gene carotenoid cluster of this organism and established that crtE and crtB are separate open reading frames with separate activities, which is the gene-level basis for rejecting the transferred GGPP synthase activity.
"Six open reading frames were found and designated the crtE, crtX, crtY, crtI, crtB, and crtZ genes in reference to the carotenoid biosynthesis genes of a photosynthetic bacterium, Rhodobacter capsulatus"
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Determined the pathway by analysing carotenoids accumulating in E. coli transformants expressing subsets of the cluster genes, placing crtB upstream of the desaturation and cyclization steps.
"The carotenoid biosynthetic pathway in Erwinia uredovora was clarified by analyzing carotenoids accumulated in E. coli transformants in which some of these six genes were expressed"
Expression of an active phytoene synthase from Erwinia uredovora and biochemical properties of the enzyme.
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Overexpressed and partially purified the crtB product from this organism and demonstrated conversion of GGPP to phytoene in vitro, with the product confirmed against authentic standards.
"A non-radioactive assay was developed that enabled the conversion of GGPP to phytoene."
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Established the cofactor requirement as ATP together with either manganese or magnesium, with no nicotinamide cofactor, which distinguishes the enzyme from NAD(P)H-dependent squalene synthases.
"The essential cofactors required were ATP in combinations with either Mn2+ or Mg2+."
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Determined a Km of 41 microM for the GGPP substrate.
"The Km value for GGPP was determined as 41 microM."
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Showed that CrtB expression depletes the host geranylgeranyl diphosphate pool and that co-expression of the separate GGPP synthase crtE relieves the resulting growth defect, establishing GGPP as substrate rather than product.
"Presumably inhibition of growth arose from the depletion of the substrate geranylgeranyl pyrophosphate (GGPP)"
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Reported inhibition by phosphate and by squalestatin, a squalene synthase inhibitor, reflecting the active-site architecture shared with squalene synthases rather than squalene synthase activity.
"Phytoene synthesis was inhibited by phosphate ions and squalestatin."
UniProt entry CRTB_PANAN (P21683)
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Records the enzymatic product as 15-cis-phytoene, with the all-trans form arising by photoisomerisation, which justifies the 15-cis specificity of GO:0046905 despite the isomer mixture observed in vitro.
"The enzyme produces 15-cis-phytoene."
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Assigns the entry to the phytoene/squalene synthase family and records the pathway as phytoene biosynthesis within carotenoid biosynthesis.
"Belongs to the phytoene/squalene synthase family."
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Notes that ATP is required for activity but does not appear to be consumed, an unresolved mechanistic point carried into the suggested experiments.
"ATP is required for the transferase activity but it does not seem"
Deep research report for Pantoea ananatis crtB
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Confirms the identity check and the GGPP-to-15-cis-phytoene assignment, and states explicitly that no localization experiment exists for this protein.
"remains inferred rather than experimentally demonstrated for P21683"
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States that no alternative-substrate panel has been reported, which is recorded here as a substrate-specificity knowledge gap.
"No rigorous alternative-substrate panel for P21683 was recovered."