Part:BBa_K2593007

xylR-PxylA-RBS-HasA
This composite part consists of a promoter, an RBS, a coding sequence of HA synthase gene, and a terminator.

xylR-PxylA (BBa_K733002): A xylose inducible promoter with its transcriptional regulator.
This part consists of an xylose inducible promoter, originated from Bacillis megaterium, which is amplified from the integration vector pAX01 and an xylose repressor gene. Promoter PxylA is located within xylose operon, originally to drive the expression of xylA (xylose isomerase coding gene) and xylB (xylulose kinase). xylR with its promoter located at upstream of xylose operon. It encodes xyl repressor which binds to xyl operator in the absence of xylose, repressing transcription activation. In the presence of glucose, glucose-6-phosphate metabolized from glucose can compete with xylose in the binding site of xylose on XylR. In addition, glucose itself is also supposed to be a low efficiency inducer for XylR (DAHL, 1997). Therefore while xylose induces transcription, the existence of glucose, to some extent, represses gene transcription.

RBS(BBa_K2593005): it’s a strong Ribosome Binding Site which is commonly used in bacteria.

HasA gene (BBa_K2593001) : HA synthase pathway In Streptococcus species, HA biosynthsis begins with the phosphorylation of glucose by hexokinase to produce the main precursor, glucose-6-phosphate (G6P).From here, HA synthesis pathway can be divided into two distinct pathways that syntheses the two building blocks of HA, glucuronic acid and N-acetylglucosamine (Fig. 2). In the first set of reactions, a-phosphoglucomutase (pgcA) converts glucose-6-phosphate to glucose-1-phosphate before a phosphate group from UTP is transferred to glucose-1-phosphate by UDP-glucose pyrophosphorylase (hasC/gtaB) to produce UDP-glucose. UDP-glucose is oxidised by UDP-glucose dehydrogenase (hasB/tuaB) to yield the first HA precursor, UDP-glucuronic acid (UDP- GlcUA).
In the second set of reactions, G6P is converted into fructose 6-phosphate (F6P) by glucose phosphate isomerase which is encoded by pgi gene. Fructose 6-phosphate (F6P) is then catalyzed stepwide to glucosamine 6-phosphate, glucosamine-1-Pand N-Acetyl Glucosamine-1-P by Glucosamine--fructose-6-phosphateaminotransferase (glmS), Phosphoglucosaminemutase (glmM) and N-acetylglucosamine-1-phosphateuridyltransferase (glmU) respectively, and eventually the second precursor, UDP-GlcNAc, was synthesized. Once the two precursors are synthesised, hyaluronan synthase (hasA) polymerises the two components in an alternate manner to produce the HA polymer.
B. Subtilis, containing all native pathway genes for the biosynthesis for the HA precursors UDP-GlcUA and UDP-GlcNAc, has been regarded as an ideal cell factory for synthetic biology manipulations in HA biosynthesis studies.