Identification of heat-stable A-factor from Myxococcus xanthus.
The asg mutants of Myxococcus xanthus fail to produce a set of related substances called A-factor. A-factor is released into the medium and is required early in fruiting body development. Lacking A-factor, the asg mutants are defective in aggregation, sporulation, and expression of most genes whose products appear later than 1 h after development is induced by starvation. Previous work has shown that these defects are reversed when A-factor, released by developing wild-type cells, is added to asg mutant cells. Part of the material in conditioned medium with A-factor activity is heat stable and dialyzable. This low-molecular-weight A-factor consists of a mixture of amino acids and peptides. Fifteen single amino acids have A-factor activity, and 11 of these are found in conditioned medium. Mixtures of amino acids have a total activity approximately equal to the sum of the activities of their constituents. Conditioned medium also contains peptides with A-factor activity. Pure peptides have A-factor activity, and their specific activities are equal to or less than the sum of the activities of their constituent amino acids. There is no evidence for a specialized A-factor peptide in conditioned medium, one with a specific activity greater than the sum of its constituent amino acids. About half of the heat-stable A-factor activity in conditioned medium can be accounted for by free amino acids, and the remaining half can be accounted for by peptides. It is argued that heat-stable A-factor induces A-dependent gene expression not by the nutritional action of amino acids but through a chemosensory circuit.
Kuspa
A
A
Department of Biochemistry, Stanford University, California 94305.
Plamann
L
L
Kaiser
D
D
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis / Q000494:pharmacology; D001681:Biological Assay; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D006133:Growth Substances / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000187:drug effects / Q000502:physiology*; D016941:Myxococcus xanthus / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology; D010455:Peptides / Q000494:pharmacology
D000596:Amino Acids; D003470:Culture Media; D006133:Growth Substances; D010455:Peptides