Variant codes:

A.123 – full Ribose utilization operon and Ribose 5-phosphate isomerase:
RbsK + RbsABCD transporter set + RbsR + RpiA, RpiB (or any one of them);

A.12 - RbsK + RpiA, RpiB (or any one of them) + any transporter set;

A.1 – RbsK + RpiA, RpiB (or any one of them) and some transport, as in Staphylococcus;

B – RbsK + RpiA, RpiB (or any one of them)

C - just Ribokinase (EC 2.7.1.15) - RbsK;

This subsystem was originally encoded by master:laikova.
Ownership of the SS was changed 11/05/07 to OlgaZ for extending and further maintenance.

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From ref.2:

It is not surprising that allose and ribose transport systems are functionally redundant because D-ribose exists primarily as a pyranose form (80%) in solution, which is presumably responsible for interacting with the periplasmic binding protein and also with the membrane components. This configuration of D-ribose is structurally analogous to that of D-allose.
Moreover, D-ribose can still be utilized when both the ribose and allose systems are absent, suggesting that other structurally related permeases provide the remaining activity of low-affinity transport.

========REFERENCES:==========

1. Poulsen TS, Chang YY, Hove-Jensen B. D-Allose catabolism of Escherichia coli: involvement of alsI and regulation of als regulon expression by allose and ribose.J Bacteriol. 1999 Nov;181(22):7126-30. PMID: 10559180

2. Kim C, Song S, Park C. The D-allose operon of Escherichia coli K-12.
J Bacteriol. 1997 Dec;179(24):7631-7. PMID: 9401019