Dictyostelium TRFA Homologous to Yeast Ssn6 Is Required for Normal Growth and Early Development

The TPR (tetratricopeptide repeat) family became widespread during evolution, having been found from bacteria to mammals. By means of restriction enzyme-mediated integration, we have identified a Dictyostelium gene (trfA) highly homologous to a Saccharomyces cerevisiae gene encoding a TPR protein, Ssn6 (Cyc8), which functions as a global transcriptional repressor for diverse genes. The deduced amino acid sequence of the Dictyostelium gene product, TRFA, contains 10 consecutive TPR units as well as Gin repeats, Asn repeats, and a region rich in Glu, Lys, Ser, and Thr, The sequences of some of the 10 TPR units in TRFA are more than 70% identical to the corresponding units in Ssn6.The trfA(-) cells produced smooth plaques on a bacterial lawn and failed to aggregate normally when stirred on a plain agar plate, Individual trfA(-) cells also failed to correctly respond to cAMP, although the adenylyl cyclase of trfA(-) cells was expressed upon starvation and activated by stimulation with cAMP as in the wild-type cells. When cultured in a rich medium in suspension, they grew more slowly and stopped growing at a lower density than the wild-type cells. Furthermore, they divided into cells of various sizes and tended to be much smaller than the wild-type cells, These pleiotropic defects of the trfA(-) cells suggest the possibility that Dictyostelium TRFA may regulate the transcription of diverse genes required for normal growth and early development.