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Myxococcus xanthus sasN encodes a regulator that prevents developmental gene expression during growth
D Xu1, C Yang, H B Kaplan
1Department of Microbiology and Molecular Genetics, The University of Texas Medical School, Houston, Texas 77030, USA.
Abstract:
Myxococcus xanthus multicellular fruiting body development is initiated by nutrient limitation at high cell density. Five clustered point mutations (sasB5, -14, -15, -16, and -17) can bypass the starvation and high-cell-density requirements for expression of the 4521 developmental reporter gene. These mutants express 4521 at high levels during growth and development in an asgB background, which is defective in generation of the cell density signal, A signal. A 1.3-kb region of the sasB locus cloned from the wild-type chromosome restored the SasB+ phenotype to the five mutants. DNA sequence analysis of the 1.3-kb region predicted an open reading frame, designated SasN. The N terminus of SasN appears to contain a strongly hydrophobic region and a leucine zipper motif. SasN showed no significant sequence similarities to known proteins. A strain containing a newly constructed sasN-null mutation and Omega4521 Tn5lac in an otherwise wild-type background expressed 4521 at a high level during growth and development. A similar sasN-null mutant formed abnormal fruiting bodies and sporulated at about 10% the level of wild type. These data indicate that the wild-type sasN gene product is necessary for normal M. xanthus fruiting body development and functions as a critical regulator that prevents 4521 expression during growth.
Insights
Mutations in Myxococcus xanthus bypass starvation and high-cell-density requirements for developmental gene expression. The SasN protein regulates fruiting body development and prevents premature gene activation during growth.
Area of Science:
- Microbiology
- Molecular Biology
- Developmental Biology
Background:
- Myxococcus xanthus development initiates under nutrient limitation and high cell density.
- Specific mutations (sasB) can bypass these requirements for developmental gene expression.
- The asgB mutation affects cell density signaling (A signal).
Purpose of the Study:
- Identify the gene responsible for the SasB phenotype.
- Characterize the function of the identified gene in M. xanthus development.
Main Methods:
- Genetic analysis of sasB mutants.
- Cloning and sequencing of the sasB locus.
- Construction and analysis of a sasN-null mutant.
- Reporter gene expression analysis (4521 reporter).
Main Results:
- A 1.3-kb region containing an open reading frame (SasN) was identified.
- SasN N-terminus has hydrophobic regions and a leucine zipper; no sequence similarity to known proteins.
- sasN-null mutants express the 4521 reporter during growth and exhibit abnormal fruiting body development and reduced sporulation.
Conclusions:
- The wild-type sasN gene product is essential for normal Myxococcus xanthus fruiting body development.
- SasN acts as a critical regulator, preventing premature expression of developmental genes during growth.