Spontaneous mutations in the ammonium transport gene AMT4 of Chlamydomonas reinhardtii.
Evidence in several microorganisms indicates that Amt proteins are gas channels for NH(3) and CH(3)NH(2), and this has been confirmed structurally. Chlamydomonas reinhardtii has at least four AMT genes, the most reported for a microorganism. Under nitrogen-limiting conditions all AMT genes are transcribed and Chlamydomonas is sensitive to methylammonium toxicity. All 16 spontaneous methylammonium-resistant mutants that we analyzed had defects in accumulation of [(14)C]methylammonium. Genetic crosses indicated that 12 had lesions in a single locus, whereas two each had lesions in other loci. Lesions in different loci were correlated with different degrees of defect in [(14)C]methylammonium uptake. One mutant in the largest class had an insert in the AMT4 gene, and the insert cosegregated with methylammonium resistance in genetic crosses. The other 11 strains in this class also had amt4 lesions, which we characterized at the molecular level. Properties of the amt4 mutants were clearly different from those of rh1 RNAi lines. They indicated that the physiological substrates for Amt and Rh proteins, the only two members of their protein superfamily, are NH(3) and CO(2), respectively.
Kim
Kwang-Seo
KS
Department of Plant and Microbial Biology, University of California, Berkeley, 94720, USA.
Feild
Eithne
E
King
Natalie
N
Yaoi
Takuro
T
Kustu
Sydney
S
Inwood
William
W
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D015152:Blotting, Northern; D002245:Carbon Dioxide / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics* / Q000502:physiology; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D003433:Crosses, Genetic; D004247:DNA / Q000737:chemistry; D005821:Genetic Techniques; D005838:Genotype; D008744:Methylamines / Q000494:pharmacology; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D016133:Polymerase Chain Reaction; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013997:Time Factors; D014158:Transcription, Genetic
D027682:Cation Transport Proteins; D008744:Methylamines; D010455:Peptides; D000644:Quaternary Ammonium Compounds; D002245:Carbon Dioxide; D012313:RNA; D004247:DNA; C027451:methylamine; D009584:Nitrogen