Ref ID : 7379
Marion Breuer, Gerald Schulte, Klaus J. Schwegmann, and Helmut J. Schmidt; Molecular Characterization of the D Surface Protein Gene Subfamily in Paramecium tetraurelia. J.Eukaryot.Microbiol. 43(4):314-322, 1996
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When Paramecium tetraurelia exresses the D serotype, detectable by serum tests, high molecular mRNA could be isolated, which corresponds to the molecular mass of the D surface protein. Using this D specific mRNA as a probe for screenings in different genomic libraries a subfamily of five similar genes was found, named alpha-51D, gamma1-51D, gamma2-51D, deruta-51D and seta-51D. Each of them is about 8-kb long, they show regions of identity to each other, and there is no evidence that any are defective genes or pseudogenes. Up to now serotype D is the only known serotype showing this phenomenon. Another novel feature is that two of the D isogenes are closely linked. The sequence for the entire coding region of the alpha-51D gene has been determined, as well as the upstream and downstream noncoding regions. Its deduced amino acid sequence shows the same characteristic cysteine periodicity displayed by all other immobilization antigen (i-ag) genes from Paramecium. However, in contrast to most other such genes, tandem repeats are missing from the 7599-bp long coding region of the alpha-51D gene. When the sequences of the type 51D genes are compared to each other, the similarity is very high and extends to coding as well as to noncoding regions. Similarity within noncoding regions is usually only observed for allelic i-ag genes. We concluded that the type D genes constitute a family to isogenes that are nonallelic. They contain slightly different consensus sequences with possible functions as regulatory regions.