A mutant of Synechococcus PCC 7942 impaired in HCO3- uptake.
An inactivation library was used to isolate high-CO2-requiring mutants of Synechococcus PCC 7942. One of them, mutant IL-7, is composed of elongated cells, some 5-15 times longer than the wild-type. IL-7 is impaired in the ability to accumulate inorganic carbon within the cells due to a lesion in HCO3- transport. Consequently, the apparent photosynthetic affinity for external inorganic carbon was about 50-100-fold lower than in the wild-type. Analysis of the genomic region modified in IL-7 demonstrated that the inactivating fragment was composed of two genomically unrelated fragments which were ligated together during the formation of the inactivation library. One of the fragments originated from a known genomic region, rbcLS, encoding ribulose 1,5-bisphosphate carboxylase/oxygenase and the other showed high homology to mutS encoding a DNA mismatch repair protein. We suggest that the primary lesion in IL-7 was in mutS and not in rbcLS, and that the phenotype of IL-7 resulted from secondary random mutations. We were unable to identify the spontaneous mutation(s) due to low transformability of IL-7. Our finding that two unrelated fragments ligated together points to possible mistakes in the identification of the function of putative genes with the aid of an inactivation library.
Ronen-Tarazi
M
M
Department of Plant Sciences, Moshe Shilo Minerva Center for Marine Biogeochemistry, Hebrew University of Jerusalem, Israel.
Shinder
V
V
Kaplan
A
A
D000595:Amino Acid Sequence; D001639:Bicarbonates / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D005838:Genotype; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype
D001639:Bicarbonates