CHARACTERIZATION OF MULTIGENE FAMILIES IN THE MICRONUCLEAR GENOME OF PARAMECIUM-TETRAURELIA REVEALS A GERMLINE SPECIFIC SEQUENCE IN AN INTRON OF A CENTRIN GENE

In Paramecium, as in other ciliates, the transcriptionally active macr onucleus is derived from the germline micronucleus by programmed DNA r earrangements, which include the precise excision of thousands of germ line-specific sequences (internal eliminated sequences, IESs), We repo rt the characterization of micronuclear versions of genes encoding Par amecium secretory granule proteins (trichocyst matrix proteins, TMPs) and Paramecium centrins, TMP and centrin multigene families, previousl y studied in the macronuclear genome, consist of genes that are co-exp ressed to provide mixtures of related polypeptides that co-assemble to form respectively the crystalline trichocyst matrix and the infracili ary lattice, a contractile cytoskeletal network, We present evidence t hat TMP and centrin genes identified in the macronucleus are also pres ent in the micronucleus, ruling out the possibility that these novel m ultigene families are generated by somatic rearrangements during macro nuclear development, No IESs were found in TMP genes, however, four IE Ss in or near germline centrin genes were characterized, The only intr agenic IES is 75 bp in size, interrupts a 29 bp intron and is absent f rom at least one other closely related centrin gene, This is the first report of an IES in an intron in Paramecium.