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Ammonium and nitrate are the primary nitrogen sources in natural environments, and are essential for growth and development in photosynthetic eukaryotes. In this study, we report on the isolation and characterization of an ammonium transporter gene ( PyAMT1 ) which performs a key function in nitrogen (N) metabolism of Pyropia yezoensis thalli. The predicted length of PyAMT1 was 483 amino acids (AAs). The AA sequence included 11 putative transmembrane domains and showed approximately 33–44% identity to algal and plant AMT1 AA sequences. Functional complementation in an AMT -defective yeast mutant indicated that PyAMT1 mediated ammonium transport across the plasma membrane. Expression analysis showed that the PyAMT1 mRNA level was strongly induced by N-deficiency, and was more highly suppressed by resupply of inorganic-N than organic-N. These results suggest that PyAMT1 plays important roles in the ammonium transport system, and is highly regulated in response to external/internal N-status. [ABSTRACT FROM AUTHOR]

We constructed a cDNA library from sterile Ulva pertusa (Ulvales, Chlorophyta), and isolated and characterized a full-length cDNA clone encoding actin. The actin (ACT) cDNA consisted of 1487 nucleotides (nt) and had an open reading frame (ORF) encoding a polypeptide of 377 amino acid (AA) residues. The ACT gene had one intron in the 5′-untranslated region and three introns in the coding region. Transcription started 26 nt downstream of the putative TATA box. A potential polyadenylation signal, TGTAG, was located 100 nt downstream of the terminator codon, TAG. Amino acid alignment with actins from various algae and land plants showed that sterile U. pertusa actin was more similar to actins from Chlorophyta, Phaeophyta, Euglenophyta, and higher plants (over 76.9%) than to actins from Rhodophyta. Southern blot analysis indicated that the sterile U. pertusa genome has only a single actin-encoding gene. Thalli grown on a 12D/12L photoperiod increased in surface area some two-fold over 24 h regardless of the nutritional conditions. The growth rate of thalli during the light period was significantly higher than that during the dark period. Northern hybridization indicated that the expression of actin mRNA was induced and repressed by the light and dark treatments, respectively. These results suggest that the U. pertusa cell division cycle has a periodicity of 24 h and that the ACT gene is highly transcribed during cell growth and development in the light period. [Copyright &y& Elsevier]

Characterizes complementary DNA clone encoding glutamate dehydrogenase in green alga, Ulva pertusa. Amino acid sequence; Nucleotide sequence; Expression of messenger RNA; Tissue distribution.