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DNA sequence of the Serratia marcescens lipoprotein gene
Abstract:
The Serratia marcescens gene for the outer membrane lipoprotein (lpp) was cloned in lambda phage vector Charon 14. The recombinant phage was very unstable, and the lpp gene with a 300-base-pair deletion at the transcription termination site was further cloned in pBR322. The DNA sequence of 834 base pairs encompassing the lpp gene was determined and compared with that of the Escherichia coli lpp gene. The sequence comparisons exhibit several unique features. (i) The promoter region is highly conserved (84% homology) and has an extremely high A+T content (78%) as in E. coli (80%). (ii) The 5' nontranslated region of the lipoprotein mRNA is also highly conserved (95% homology). (iii) In the DNA sequence corresponding to the signal peptide of this secretory protein, there are three drastic changes, including addition of one base pair and deletion of four base pairs in S. marcescens as compared to E. coli. The resultant alterations in the amino acid sequence, however, do not change the basic properties of the signal peptide, which are assumed to be essential for its function in the secretory mechanism. (iv) The DNA sequence from the amino terminus to the 51st residue of the mature lipoprotein is highly conserved (95% homology) and there is no amino acid substitution. (v) The DNA sequence corresponding to the seven amino acid residues at the carboxyl terminus has only 42% homology, resulting in four amino acid substitutions. (vi) Within the section of 40 base pairs beginning with the termination codon (UAA) and ending immediately before the oligo(T) transcription termination site in the E. coli lpp gene, there is about 60% homology. However, after this section, there is no obvious homology between the two sequences, probably because of a deletion of 300 base pairs at this region. (vii) Seven stable stem-and-loop structures could be formed in the mRNA region. (viii) Alterations in the third position of codons used in the lpp gene suggest that the gene has evolved somewhat differently from other genes in S. marcescens.
Insights
Researchers compared the Serratia marcescens lipoprotein (lpp) gene with E. coli's, finding high conservation in key regions like the promoter and signal peptide. Despite some changes, the lipoprotein
Area of Science:
- Molecular Biology
- Genetics
- Bacterial Outer Membrane Proteins
Background:
- The outer membrane lipoprotein (lpp) is a crucial component of bacterial cell envelopes.
- Understanding the genetic basis of lpp in different bacterial species aids in comparative genomics and evolutionary studies.
Purpose of the Study:
- To clone and sequence the Serratia marcescens lipoprotein (lpp) gene.
- To compare the S. marcescens lpp gene sequence with that of Escherichia coli.
- To identify conserved and divergent regions and their potential functional implications.
Main Methods:
- Cloning of the S. marcescens lpp gene into lambda phage vector Charon 14 and subsequently into pBR322.
- DNA sequencing of the 834 base pair region encompassing the lpp gene.
- Comparative sequence analysis between S. marcescens and E. coli lpp genes.
Main Results:
- High homology (84%) was observed in the promoter region, with similar high A+T content.
- The 5' non-translated region and the signal peptide sequence showed significant conservation (95% and functional similarity, respectively).
- The mature lipoprotein sequence was highly conserved up to the 51st residue, with divergence in the carboxyl terminus and downstream regions due to deletions.
Conclusions:
- The S. marcescens lpp gene shares significant sequence homology with E. coli, particularly in functionally important regions.
- Sequence variations, especially in the signal peptide and carboxyl terminus, suggest evolutionary divergence.
- The conserved regions highlight the essential roles of these parts of the lipoprotein in bacterial structure and function.