Subsystem: Threonine and Homoserine Biosynthesis
This subsystem's description is:
The pathway of threonine biosynthesis has been shown to be similar in all micro-organisms ( see Diagram). However, the organization of the genes for threonine biosynthesis enzymes is different in different micro-organisms.
In enterobacteria and in plants aspartate kinase (ASK) and homoserine dehydrogenase (HDH) activities are present in the same polypeptide, ThrA. The thrA gene is organized in an operon along with the genes for homoserine kinase (HK; thrB) and HDH (thrC), and the gene for aspartate semialdehyde dehydrogenase (asd) is not linked to them.
A different type of thr gene organization is found in Gram-positive bacteria. In L. lactis, Brevibacterium lactofermentum and Corynebacterium glutamicum the hom and thrB genes are linked and thrC is located elsewhere in the chromosome.
In Bacillus spp. hom-thrC-thrB are clustered together.
In some Gram-positive bacteria studied so far (Mycobacterium spp., Corynebacterium spp.) the genes for ASK (ask) and aspartate semialdehyde dehydrogenase (ASD) are organized in an operon; in others, and in all Gram-negative bacteria studied so far, these genes are not linked.
The third type of threonine biosynthesis gene organization is found in Gram-negative bacteria other than enterobacteria. In these hom and thrC are clustered together and thrB is located elsewhere in the chromosome.
1.0 – complete pathway of threonine biosynthesis (thrA-asd-hom-thrC-thrB genes);
1.1 - complete pathway of threonine biosynthesis + Aspartate aminotransferase;
1.x - incomplete pathway of threonine biosynthesis;
For more information, please check out the description and the additional notes tabs, below
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