Transcriptional Regulation of the MS2 Gene of Paramecium tetraurelia

Abstract

MS2 of Paramecium tetraurelia is the gene that we have cloned as one expressed at much higher levels in a short-lived mutant than in its parental wild-type stock and have characterized its expression to be enhanced with increased clonal age of the wild-type stock. This gene has been found to be preferentially expressed also in paramecia undergoing autogamy which is one of the termination modes of the Paramecium clonal life span. Here we investigated the transcriptional mechanism for the MS2 expression in light of its possible causal relationship to the Paramecium clonal life span. DNA-protein binding analyses of the upstream of the MS2 gene identified a stretch of DNA sequence that interacted specifically with macronuclear proteins prepared from the MS2- expressing mutant. The DNA sequence was mapped to the 33 bp between — 335 and — 303, counting from the initiation position of MS2 transcription. A protein, 15,000 in molecular mass, with a binding ability for this DNA element was purified to homogeneity from the macronuclear proteins by a chromatography using the specific DNA-protein interaction. In vitro transcriptional analyses revealed that both the purified protein and its target DNA domain are essential for increased synthesis of the MS2 transcript. These results showed that the DNA-protein interaction is required for induction of the MS2 expression.