We have studied the light-dependent expression of the Chlamydomonas reinhardtii csbp gene encoding sedoheptulose-1,7-bisphosphatase (SBPase), an enzyme of the pentose-phosphate pathway. Expression studies using light/dark-synchronized cultures revealed that csbp mRNA abundance increases significantly during illumination. We have used a 1.4 kb region upstream of the csbp gene in transcriptional fusions to the homologous arylsulfatase-encoding reporter gene (ars). In transformants carrying the chimeric csbp/ars reporter gene, arylsulfatase activity is detected in the absence of sulfate, a condition under which the endogenous ars gene is repressed. Moreover, ars mRNA accumulation is dramatically stimulated by light, indicating that 1.4 kb of the csbp 5′-untranslated region are sufficient to confer light-dependent expression on the ars reporter gene.