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Journal of Bacteriology, December 2006, p. 8005-8012, Vol. 188, No. 23
0021-9193/06/$08.00+0     doi:10.1128/JB.01101-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

A Member of the Second Carbohydrate Uptake Subfamily of ATP-Binding Cassette Transporters Is Responsible for Ribonucleoside Uptake in Streptococcus mutans

Microbiology, King's College London Dental Institute, London, United Kingdom

Received 25 July 2006/ Accepted 12 September 2006

Streptococcus mutans has a significant number of transporters of the ATP-binding cassette (ABC) superfamily. Members of this superfamily are involved in the translocation of a diverse range of molecules across membranes. However, the functions of many of these members remain unknown. We have investigated the role of the single S. mutans representative of the second subfamily of carbohydrate uptake transporters (CUT2) of the ABC superfamily. The genetic context of genes encoding this transporter indicates that it may have a role in ribonucleoside scavenging. Inactivation of rnsA (ATPase) or rnsB (solute binding protein) resulted in strains resistant to 5-fluorocytidine and 5-fluorouridine (toxic ribonucleoside analogues). As other ribonucleosides including cytidine, uridine, adenosine, 2-deoxyuridine, and 2-deoxycytidine protected S. mutans from 5-fluorocytidine and 5-fluorouridine toxicity, it is likely that this transporter is involved in the uptake of these molecules. Indeed, the rnsA and rnsB mutants were unable to transport [2-¹⁴C]cytidine or [2-¹⁴C]uridine and had significantly reduced [8-¹⁴C]adenosine uptake rates. Characterization of this transporter in wild-type S. mutans indicates that it is a high-affinity (K_m = 1 to 2 µM) transporter of cytidine, uridine, and adenosine. The inhibition of [¹⁴C]cytidine uptake by a range of structurally related molecules indicates that the CUT2 transporter is involved in the uptake of most ribonucleosides, including 2-deoxyribonucleosides, but not ribose or nucleobases. The characterization of this permease has directly shown for the first time that an ABC transporter is involved in the uptake of ribonucleosides and extends the range of substrates known to be transported by members of the ABC transporter superfamily.

Published ahead of print on 22 September 2006.

This article has been cited by other articles:

• Webb, A. J., Homer, K. A., Hosie, A. H. F. (2008). Two Closely Related ABC Transporters in Streptococcus mutans Are Involved in Disaccharide and/or Oligosaccharide Uptake. J. Bacteriol. 190: 168-178 [Abstract] [Full Text]  
• Ajdic, D., Pham, V. T. T. (2007). Global Transcriptional Analysis of Streptococcus mutans Sugar Transporters Using Microarrays. J. Bacteriol. 189: 5049-5059 [Abstract] [Full Text]  
• Webb, A. J., Homer, K. A., Hosie, A. H. F. (2007). A Phosphoenolpyruvate-Dependent Phosphotransferase System Is the Principal Maltose Transporter in Streptococcus mutans. J. Bacteriol. 189: 3322-3327 [Abstract] [Full Text]