期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1979
卷号：76
期号：1
页码：209-213
DOI：10.1073/pnas.76.1.209
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Myxococcus xanthus is a Gram-negative bacterium that has a complex life cycle including a temporal sequence of cellular aggregation, mound formation, and myxosporulation. During development, protein S (molecuar weight 23,000) is induced and accumulates in very large amounts. Protein S was found in the soluble fraction of early developmental extracts and in the insoluble fraction in later extracts. This insoluble form of protein S can be solubilized by the addition of 1 M NaCl at 0{degrees}C to extracts from aggregated cells (mound stage) or by the addition of 1 M NaCl at 30{degrees}C to mature spores. Salt extraction (1 M NaCl) of protein S from mature spores was partially inhibited by the addition of Mg2+ and almost completely inhibited by the addition of Ca2+. The viability of spores was not changed by a salt extraction that removed their protein S. Examination of thin sections of mature spores and extracted spores by electron microscopy suggested that the protein S-deficient spores lacked a spore surface coat about 300 A thick. Purified protein S will spontaneously self-assemble onto protein S-deficient spores after removal of the NaCl by dialysis or by addition of 10 mM Ca2+ to undialyzed samples. Glycerol-induced spores did not contain protein S and did not serve as primers for assembly of protein S. Quantitation of the self-assembly process showed almost stoichiometric binding of protein S to the protein S-deficient spores until saturation at 3.3 x 106 molecules per spore, a value 1.35 times higher than the normal level of proteins S found in mature spores. Protein S in the "reconstituted" spores was as protease resistant and sonication resistant as the protein S of native spores. Electron microscopy of the reconstituted spores revealed the assembly of new material on the spore surface. Adjacent spores were sometimes observed to be fused to each other through a common protein S layer. These results suggest that protein S serves a function in spore--spore interaction in the fruiting body.
关键词：spores ; fruiting body ; sodium dodecyl sulfate gel electrophoresis ; calcium ion
