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MSG gene cluster encoding major cell surface glycoproteins of rat Pneumocystis carinii
1Department of Tumor Biology, University of Tokyo, Japan.
Abstract:
The MSG genes of Pneumocystis carinii encode major cell surface glycoproteins of multi-gene families and play crucial roles in the pathobiology of P. carinii pneumocystosis. The 11,370-bp chromosomal DNA encoding MSG was cloned and sequenced. It contained three open reading frames in tandem repeat, MSG99, MSG100 and ORF-3. MSG99 and MSG100 shared 39% protein sequence identity and belonged to the same MSG family, regardless of the internal ca. 1,000-bp deletion in MSG99. ORF-3 encodes a putative 47,820-Da protein and had no sequence similarities to MSG molecules or any known proteins. However, the ORF-3 protein was rich in proline residues and highly hydrophilic except for the C-terminal region, which seemed to be an anchoring sequence in the cell membrane. Northern and Southern blot hybridization analyses revealed a 3-kb ORF-3 transcript as well as multiple DNA fragments carrying the MSG and ORF-3 sequences. These results strongly suggested that diverse MSG genes are clustered in tandem repeats and these clusters involve ORF-3. The possible association of ORF-3 protein in the cell membrane is discussed.
Insights
Pneumocystis carinii major surface glycoproteins (MSG) genes are clustered with ORF-3. This study cloned and sequenced the DNA encoding MSG, revealing tandem repeats and suggesting ORF-3
Area of Science:
- Microbiology
- Molecular Biology
- Parasitology
Background:
- Pneumocystis carinii major surface glycoproteins (MSG) are key to P. carinii pneumocystosis.
- MSG proteins are encoded by multi-gene families and are crucial cell surface components.
Purpose of the Study:
- To clone and sequence the chromosomal DNA encoding MSG.
- To investigate the organization and potential function of MSG gene clusters, including associated open reading frames (ORFs).
Main Methods:
- Chromosomal DNA cloning and sequencing of MSG-encoding regions.
- Bioinformatic analysis of open reading frames (ORFs) and protein sequences.
- Northern and Southern blot hybridization to analyze gene expression and organization.
Main Results:
- A 11,370-bp DNA sequence containing three tandem ORFs (MSG99, MSG100, ORF-3) was identified.
- MSG99 and MSG100 showed 39% protein identity, belonging to the same MSG family.
- ORF-3 encodes a proline-rich, hydrophilic protein with a potential membrane-anchoring C-terminal region; its transcript is 3 kb.
Conclusions:
- Diverse MSG genes are likely clustered in tandem repeats, involving ORF-3.
- The ORF-3 protein's characteristics suggest a role in cell membrane association.
- Understanding MSG gene organization provides insights into P. carinii pathobiology.