| When cells of Anacystis nidulans are deprived of a sulfur source they begin to acclimate to the new conditions. Among other responses, there is an increase in the capacity of sulfur-starved cells to take up sulfate. While the apparent V{dollar}sb{lcub}rm max{rcub}{dollar} for sulfate uptake increases at least ten-fold after 24 hours of sulfur deprivation, the Km remains approximately 1 {dollar}mu{dollar}M. The increased capacity to take up sulfate is accompanied by an increased abundance of four cytoplasmic membrane polypeptides of 43, 42, 36 and 17 kDa. These changes are specific; they do not occur response to nitrogen or phosphorus deprivation.; Dramatic changes also occur in the soluble protein fraction of A. nidulans in response to sulfur deprivation. Three polypeptides of Mr 36.5, 33, and 28.5 kDa accumulate to high levels in sulfur-starved, but not nitrogen- or phosphorus-starved cells. The 33.5 kDa polypeptide has been purified and two different strategies have been used in an attempt to clone its structural gene. A portion of its N-terminal sequence was used to design an oligonucleotide probe for screening an EMBL3 genomic library. Antibody raised against the 33.5 kDa polypeptide was used to screen an expression library. One clone, obtained by the latter method, encodes a sulfur-regulated transcript.; An 8.3 kbp region, homologous to the sulfate permease locus of Salmonella typhimurium, has been cloned from A. nidulans. This region encodes 5 transcripts which become much more abundant in response to sulfur deprivation. Mutations introduced into this region by insertional inactivation result in cysteine auxotrophy, deficiencies in sulfate transport, and changes in the expression of sulfur-starvation proteins.; Alternate sources of sulfur were tested for their ability to support A. nidulans and for their effect on the response to sulfur deprivation. This has allowed us to develop a strategy using selenate to select for mutants defective in sulfate assimilation. |
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