The mutually exclusive expression of the 51A and 51B surface antigens of Paramecium tetraurelia
Abstract
Paramecium tetraurelia stock 51 can express at least 11 different types of surface antigens, yet only a single type is found on the surface of the cell at any one time. Out of the 11 types, the 51A and 51B genes have been selected for study due to the availability of cloned versions of the 51A and 51B genes and the corresponding A-, B-deletion mutant cell lines. Analysis of wild-type stock 51 Paramecium revealed that the 51A and 51B surface antigen genes are regulated at the level of transcription. Using the cloned 51A and 51B surface antigen genes and the corresponding double mutant, a cotransformation approach was developed to address the molecular mechanisms of differential regulation. Deletion analysis of the 51A gene upstream region demonstrated that 225 base pairs of sequence are sufficient for 51A expression but 200 base pairs are not adequate for normal expression. Surprisingly, fusion gene experiments substituting regions of the 51B gene into the 51A gene showed that although upstream sequences are necessary for transcriptional activity they are not sufficient to regulate differential transcriptional control. However, substitution of sequences from the 5$\sp\prime$ coding region of the 51B gene allowed a chimeric gene to be coexpressed with wild-type 51B. In effect, this situation was a violation of mutual exclusion and suggests that sequences within the 5$\sp\prime$ coding region of surface antigen genes are required for mutually exclusive transcriptional control.
Degree
Ph.D.
Advisors
Forney, Purdue University.
Subject Area
Biochemistry|Microbiology|Molecular biology|Immunology
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