Transcriptional activator of the arabinanolytic system. Involved in the regulation of extracellular arabinanolytic genes and in the regulation of the intracellular activities of L-arabinose catabolic genes in the pentose catabolic pathway (PCP) in response to the presence of L-arabinose. Shows no growth on L-arabinose and strong grwoth reduction on arabinan and arabinogalactan.