PHYLOGENETIC-RELATIONSHIPS AMONG HYPOTRICHOUS CILIATES DETERMINED WITH THE MACRONUCLEAR GENE ENCODING THE LARGE, CATALYTIC SUBUNIT OF DNA-POLYMERASE-ALPHA

The complete macronuclear DNA polymerase a gene, previously sequenced in Oxytricha nova, has been cloned from a genomic macronuclear library and sequenced for the hypotrich O. trifallax, Macronuclear DNA clones of DNA polymerase alpha encoding similar to 1000 amino acids, or appr oximately two-thirds of the open reading frame, have been obtained by PCR and sequenced for Halteria grandinella, Helosticha species, Paraur ostyla viridis, Pleurotricha lanceolata, Stylonychia lemnae Teller, St y. mytilus, Uroleptus gallina, and Urostyla grandis. Phylogenetic rela tionships inferred from DNA polymerase or amino acid sequences have be en used to clarify taxonomic relationships previously determined by mo rphology of the cell cortex. Hypotrich phylogenies based on DNA polyme rase a amino acid sequences are incongruent with morphological and oth er molecular phylogenies. Based upon these data, we assert that, contr ary to morphological data, O. nova and O. trifallax are different spec ies, and we propose that the oligotrich Halteria grandinella be reclas sified as a hypotrich. This work also extends the available data base of eukaryotic DNA polymerase a sequences, and suggests new amino acid sequence targets for mutagenesis experiments to continue the functiona l dissection of DNA pol a biochemistry at the molecular level.