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The ste3 pheromone receptor gene of Pneumocystis carinii is surrounded by a cluster of signal transduction genes.

ABSTRACT: Although the clinical aspects of Pneumocystis carinii pneumonia are well characterized, the basic biology of the causative organism is poorly understood. Most proposed life cycles of P. carinii include both asexual and sexual replicative cycles. The two most prominent morphological forms are a trophic form, thought to undergo asexual replication by binary fission, and a cystic form or ascus containing intracystic bodies or ascospores, the products of sexual replication. To facilitate the Pneumocystis genome project, a P. carinii f. sp. carinii genomic cosmid library and an additional lambda cDNA library were generated. A partial expressed sequence tag database, created as part of the genome project, revealed the transcription of meiosis-specific genes and other genes related to sexual reproduction. The ortholog of Ste3, an a-factor pheromone receptor, was cloned and genes surrounding the ste3 locus were examined. Clustered around the ste3 gene are genes encoding elements functional in the pheromone response signal transduction cascade of model fungal organisms. These include the Ste20 protein kinase, the Ste12 homoeodomain transcriptional regulator, a potential pheromone mating factor, and other DNA-binding proteins. The genomic organization of the ste3 locus bears significant similarity to that of the mating locus recently described in Cryptococcus neoformans. The P. carinii genome contains much of the genetic machinery necessary for pheromone responsiveness, and these data support the existence of a sexual replication cycle.

SUBMITTER: Smulian AG

PROVIDER: S-EPMC1461555 | biostudies-other | 2001 Mar

REPOSITORIES: biostudies-other

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The ste3 pheromone receptor gene of Pneumocystis carinii is surrounded by a cluster of signal transduction genes.

Smulian A G AG Sesterhenn T T Tanaka R R Cushion M T MT

Genetics 20010301 3

Although the clinical aspects of Pneumocystis carinii pneumonia are well characterized, the basic biology of the causative organism is poorly understood. Most proposed life cycles of P. carinii include both asexual and sexual replicative cycles. The two most prominent morphological forms are a trophic form, thought to undergo asexual replication by binary fission, and a cystic form or ascus containing intracystic bodies or ascospores, the products of sexual replication. To facilitate the Pneumoc ...[more]

PMID: 11238389

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Project description:BackgroundThe relationship between the parasitic fungus Pneumocystis carinii and its host, the laboratory rat, presumably involves features that allow the fungus to circumvent attacks by the immune system. It is hypothesized that the major surface glycoprotein (MSG) gene family endows Pneumocystis with the capacity to vary its surface. This gene family is comprised of approximately 80 genes, which each are approximately 3 kb long. Expression of the MSG gene family is regulated by a cis-dependent mechanism that involves a unique telomeric site in the genome called the expression site. Only the MSG gene adjacent to the expression site is represented by messenger RNA. Several P. carinii MSG genes have been sequenced, which showed that genes in the family can encode distinct isoforms of MSG. The vast majority of family members have not been characterized at the sequence level.ResultsThe first 300 basepairs of MSG genes were subjected to analysis herein. Analysis of 581 MSG sequence reads from P. carinii genomic DNA yielded 281 different sequences. However, many of the sequence reads differed from others at only one site, a degree of variation consistent with that expected to be caused by error. Accounting for error reduced the number of truly distinct sequences observed to 158, roughly twice the number expected if the gene family contains 80 members. The size of the gene family was verified by PCR. The excess of distinct sequences appeared to be due to allelic variation. Discounting alleles, there were 73 different MSG genes observed. The 73 genes differed by 19% on average. Variable regions were rich in nucleotide differences that changed the encoded protein. The genes shared three regions in which at least 16 consecutive basepairs were invariant. There were numerous cases where two different genes were identical within a region that was variable among family members as a whole, suggesting recombination among family members.ConclusionA set of sequences that represents most if not all of the members of the P. carinii MSG gene family was obtained. The protein-changing nature of the variation among these sequences suggests that the family has been shaped by selection for protein variation, which is consistent with the hypothesis that the MSG gene family functions to enhance phenotypic variation among the members of a population of P. carinii.

Dataset Information

The ste3 pheromone receptor gene of Pneumocystis carinii is surrounded by a cluster of signal transduction genes.

Publications

The ste3 pheromone receptor gene of Pneumocystis carinii is surrounded by a cluster of signal transduction genes.

Similar Datasets

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