In search of the jumyo gene, a putative gene that specifies the clonal life span of Paramecium tetraurelia, we previously compared gene expression profiles between young wild-type stock 51 and the short life span jumyo mutant d4-SL4 by the differential display technique, and detected four differentially expressed genes. In this study, assuming that expression of the jumyo gene is continuously altered throughout the clonal life span, we examined the transcriptional level of the four genes in the process of clonal aging, but none of them presented such an alteration. Thus, we again screened expressed genes of the two strains using another strategy, cDNA subtraction, and successfully isolated three different genes that show age-dependent expression patterns as expected. Of these three genes, one was specific to young wild-type cells and found to code for the 51A surface protein. The other two were preferentially transcribed in the jumyo mutant, of which one was the α-51D surface protein gene.