Complete sequence of the staphylococcal gene encoding protein A. A gene evolved through multiple duplications

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• Staphylococcus aureus protein A is a surface protein with significant biological relevance.
• Understanding the genetic basis of protein A is crucial for its biotechnological applications.

Purpose of the Study:

• To isolate and characterize the gene encoding Staphylococcus aureus protein A.
• To determine the complete nucleotide sequence of the protein A gene and its flanking regions.
• To elucidate the structural features and potential evolutionary origins of the protein A gene.

Main Methods:

• Molecular cloning techniques were used to isolate the gene.
• Subcloning into Escherichia coli facilitated functional expression.
• High-throughput sequencing determined the complete nucleotide sequence of the 1.8-kilobase insert.
• Bioinformatic analysis identified open reading frames, palindromic structures, and repeated units.

Main Results:

• A functional protein A was expressed in Escherichia coli from a 1.8-kilobase insert.
• The complete nucleotide sequence revealed an open reading frame of 1527 nucleotides, encoding a 509-amino acid preprotein.
• The gene is flanked by palindromic structures and T-rich regions, indicative of transcriptional termination signals.
• Extensive internal homologies were identified, including five repeated 58-amino acid units (IgG binding) and twelve repeated 8-amino acid units (cell wall binding).
• Silent mutations predominated in repeated regions, suggesting evolutionary pressure for amino acid sequence conservation.

Conclusions:

• The Staphylococcus aureus protein A gene has been successfully isolated and sequenced.
• The gene structure suggests monocistronic mRNA transcription and provides insights into its evolutionary development.
• The identified repeated units are likely responsible for protein A's functional properties, such as IgG and cell wall binding.