PTF1 ENCODES AN ESSENTIAL PROTEIN IN SACCHAROMYCES-CEREVISIAE, WHICH SHOWS STRONG HOMOLOGY WITH A NEW PUTATIVE FAMILY OF PPIASES

Complementation of a temperature sensitive mutant of the yeast Sacchar omyces cerevisiae resulted in the isolation of PTF1 (processing/termin ation factor 1), an essential gene encoding a putative 3'-end processi ng or transcription termination factor of pre-mRNAs. Ptf1p shows signi ficant homology to a newly discovered family of PPIases. This family i s characterized by its insensitivity to immunosuppressive drugs and th e lack of homology with cyclophilins and FK-506 binding proteins [Rahf eld et al, (1994) FEES Lett, 352, 180-184]. Should Ptf1p display PPIas e activity, it would be the first characterized, eukaryotic member of this putative family, which is essential for growth.