Chromosomal rearrangement generating a composite gene for a developmental transcription factor

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Differential gene expression in Bacillus subtilis sporulation is regulated by RNA polymerase sigma factors.
• Sigma K (sigma 27) is a key sigma factor involved in mother cell gene expression during sporulation.
• The sigma K factor was initially thought to be solely encoded by the spoIVCB gene.

Purpose of the Study:

• To elucidate the genetic basis of sigma K factor production in Bacillus subtilis.
• To investigate the role of spoIVCB and spoIIIC genes in sigma K factor formation.
• To understand the mechanism of cell type-specific gene regulation during bacterial development.

Main Methods:

• Analysis of the spoIVCB gene sequence and its protein product.
• Identification of the spoIIIC gene and its role in sigma K factor synthesis.
• Investigation of site-specific recombination between spoIVCB and spoIIIC during sporulation.

Main Results:

• The spoIVCB gene is a truncated gene encoding only the N-terminal half of sigma K.
• The C-terminal half of sigma K is encoded by the spoIIIC gene.
• SpoIVCB and spoIIIC undergo in-frame, site-specific recombination during sporulation, forming the complete sigma K gene.

Conclusions:

• Sigma K factor is generated through a unique DNA rearrangement involving spoIVCB and spoIIIC.
• This chromosomal DNA rearrangement ensures sigma K's selective presence in the mother cell.
• This mechanism serves as a model for generating cell-type-specific regulatory proteins in differentiating cells.