Identification of short promoter regions involved in the transcriptional expression of the nitrate reductase gene in Chlamydomonas reinhardtii
Chlamydomonas reinhardtii produces a periplasmic arylsulfatase in response to sulfur deprivation. We have isolated and sequenced arylsulfatase cDNAs from a λ gt11 expression library. The amino acid sequence of the protein, as deduced from the nucleotide sequence, has features characteristic of secreted proteins, including a signal sequence and putative glycosylation sites. The gene has a broad codon usage with seven codons, all having A residues in the third position, not previously observed in C. reinhardtii genes. Arylsulfatase transcription is tightly regulated by sulfur availability. The ∼2.7 kb arylsulfatase transcript is very susceptible to degradation, disappearing in less than an hour after sulfur starved cells are administered either sulfate or α-amanitin. The accumulation of the arylsulfatase transcript is also suppressed by the addition of cycloheximide. Transcription initiation from the arylsulfatase gene occurs ∼ 100 bp upstream of the initiation codon, in a region that is 5′ to a 43 bp imperfect inverted repeat. Preceding the transcription start site are sequences similar to those present in promoter regions of other genes from C. reinhardtii.