CHARACTERIZATION OF TRANSCRIPTION INITIATION, TRANSLATION INITIATION,AND POLY(A) ADDITION SITES IN THE GENE-SIZED MACRONUCLEAR DNA-MOLECULES OF EUPLOTES

The DNA in the transcriptionally active macronucleus of the hypotricho us ciliate Euplotes crassus exists as short, linear molecules with eac h molecule encoding a single genetic function. Previous work has indic ated that coding regions occupy the majority of macronuclear DNA molec ules. In the present study we have defined the transcription initiatio n sites and poly(A) addition sites for a number of different macronucl ear genes in Euplotes crassus. Our results indicate that mature transc ripts represent all but similar to 100-200 bases of the non-telomeric sequences in macronuclear DNA molecules. We have also examined the seq uences in the vicinity of transcription start sites, poly(A) addition sites, and translation initiation sites for Euplotes species genes in an attempt to define the cis-acting elements that control these proces ses. Our results indicate that some of the common sequence elements kn own to control these processes in higher eukaryotes are likely not uti lized by Euplotes genes. The data do indicate the presence of other co nserved sequences both preceding and at the site of poly(A) addition, as well as at the site of translation initiation. These conserved sequ ences may serve an analogous role in these organisms. Finally, we have found that most macronuclear DNA molecules have transcription initiat ion sites within 30 bp of the telomere, suggesting that the telomere m ay play a role in promoting transcription.