Structure and developmentally controlled DNA processing of the B type surface protein gene in Paramecium tetraurelia
Abstract
Paramecium tetraurelia contains two types of nuclei, a diploid germinal micronucleus and a large transcriptionally active macronucleus. The macronuclear genome is formed from the micronuclear DNA during sexual reproduction. Previous studies of the non-Mendelian mutant called d48 have shown that the correct processing of the A type variable surface protein gene is dependent on a copy of the A gene in the old macronucleus. It is not clear if this is a general feature that controls the formation of the Paramecium macronuclear genome, or if it is a unique feature of the A locus. My work has focused on the genetic and molecular characterization of the gene encoding the B type variable surface protein. The 7,182 nucleotide open reading frame contains no introns and encodes a cysteine-rich protein. The cysteine residues define a periodic structure which has been found in all variable surface proteins analyzed to date. I have used the cloned B gene as a tool to study macronuclear development. My hypothesis is that a cell which contains the wild-type B gene in its micronucleus, but lacks the macronuclear B gene, will be unable to process the B gene into the next macronuclear generation. Using micronuclear transplantation, a mutant strain was constructed that contains a wild-type micronucleus, but has macronuclear deletions of the A and B genes. I demonstrate that the created mutant is d48-like in three respects: (1) it cannot process the A or B gene into its developing macronucleus, (2) it inherits both the A and B genes in a non-Mendelian fashion and (3) macronuclear transformation of the cloned genes rescues the mutation in a gene specific manner. The features of this A-B-non-Mendelian mutant demonstrate that the regulation of macronuclear DNA processing is sequence specific, and this type of regulation may be a general feature that affects much of the Paramecium genome.
Degree
Ph.D.
Advisors
Forney, Purdue University.
Subject Area
Molecular biology|Genetics
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.