High-affinity L-arabinose transport operon. Gene product expression and mRNAs.

Various portions of the "high-affinity" L-arabinose transport operon were cloned into the plasmid expression vector pKK223-3 and the operon-encoded protein products were identified. The results indicate that three proteins are encoded by this operon. The first is a 33,000 Mr protein that is the product of the promoter-proximal L-arabinose binding protein coding sequence, araF. A 52,000 Mr protein is encoded by sequence 3' to araF and has been assigned to the araG locus. The sequence 3' to araG encodes a 31,000 Mr protein that has been assigned to the araH locus. Both the araG and araH gene products are localized in the membrane fraction of the cell, implying a role in the membrane-associated complex of the high-affinity L-arabinose transport system. Nuclease S1 protection studies indicate that two operon message populations are present in the cell, a full-length operon transcript and a seven- to tenfold more abundant binding protein-specific message. The relative abundance of these two message populations correlates with the differential expression of the binding protein and the membrane-associated proteins of the transport system.