DEVELOPMENTALLY-REGULATED, LOW ABUNDANCE TEC ELEMENT TRANSCRIPTS IN EUPLOTES-CRASSUS - IMPLICATIONS FOR DNA ELIMINATION AND TRANSPOSITION

During macronuclear development in the ciliated protozoan, Euplotes cr assus, >105 Tec elements are precisely eliminated from the genome in a 2 - 4 h time interval, generating extrachromosomal circular forms of the elements. Various models have proposed a transposition-based mecha nism for this excision. We have tested this hypothesis by determining the abundance of transcripts of Tec element open reading frames (ORFs) and the timing of their appearance. Transcripts are very low in abund ance and are only detected by PCR amplification techniques. Thus, the low levels of transcripts argue against the participation of element-e ncoded functions in the Tec element elimination process. The element t ranscripts are only detected in RNA samples from mated cells, indicati ng that the micronucleus and/or developing macronucleus are transcript ionally active during the sexual phase of the life cycle. The transcri ption detected could allow a low level of germline-specific transposit ion for these elements.