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Biomedical subjects

C L Jahn

Publications and source records attributed to C L Jahn.

11 recordsLinked to original sources
PubMed1991

Overamplification of macronuclear linear DNA molecules during prolonged vegetative growth of Oxytricha nova.

During prolonged vegetative growth of a clonal line of Oxytricha nova, several macronuclear linear DNA molecules increased greatly in copy number over the rest of the approx. 24,000 kinds of molecules comprising the macronuclear genome. One of the amplified sequences was the linear DNA molecule encoding rRNA (rDNA). We have cloned and sequenced the other, smaller, amplified molecules and found that they comprise a gene family, with different allelic versions of one of the family members being amplified. Thus, increased replication is a general property of the molecules comprising this gene family. To date, no function has been assigned to these genes; thus, whether the amplification of these sequences has functional significance is unknown. The rDNA molecule and the two small amplified sequences increased 11-, 24- and 107-fold, respectively, during clonal growth of this line, eventually comprising up to 15% of the macronuclear DNA molecules. Seven other macronuclear DNA molecules did not vary substantially in copy number at different times during the clonal growth of this strain. Analysis of cell-to-cell differences in copy numbers in this clonally aged strain indicated more extensive variation than is evident when large populations from different times are compared.

Amino Acid Sequence↗
PubMed1991

Developmentally controlled genomic rearrangements in ciliated protozoa.

The ciliated protozoa undergo an extensive genome reorganization during the course of forming a transcriptionally active macronucleus. The process includes numerous chromosome fragmentation and DNA breakage and rejoining events. Recent work indicates that transposable elements play a role in the process.

Animals↗
PubMed1991

Tec2, a second transposon-like element demonstrating developmentally programmed excision in Euplotes crassus.

The analysis of a repetitive DNA interruption of the micronuclear precursor to a 0.85-kb macronuclear gene in the hypotrich Euplotes crassus has led to the identification of a second transposon-like element named Tec2. Two copies of this element, one inserted into the other, compose the interruption. The Tec2 element resembles the previously characterized Tec1 element in overall size, copy number, length, and extreme terminal sequence of its inverted repeats and in the apparent use of a 5'-TA-3' target site. In addition, extrachromosomal circular forms of Tec2 appear in DNA isolated from cells undergoing macronuclear development at the same time and with the same conformation as extrachromosomal circular forms of Tec1. These similarities suggest that the Tec1 and Tec2 elements may be under the same type of regulation during macronuclear development.

Animals↗
PubMed1989

Developmentally coordinated en masse excision of a highly repetitive element in E. crassus.

The E. crassus Tec1 element is present in greater than 10(4) copies in the micronuclear genome but is absent from the macronuclear genome. During formation of a macronucleus from a micronucleus, a majority of the Tec1 elements appear as extrachromosomal circles. The circular and integrated forms of Tec1 have been characterized by restriction mapping to produce consensus maps and by sequence analysis of the element's termini. The circular forms are resistant to BAL31 and have the restriction map expected if the element excises at the end of its inverted repeats. DNA sequence analysis of a circular form confirms that the inverted repeats are in a head-to-head configuration. Excision of Tec1 occurs very early during macronuclear development as the DNA begins to replicate to form polytene chromosomes.

Animals↗
PubMed1989

Actin, tubulin and H4 histone genes in three species of hypotrichous ciliated protozoa.

In hypotrichous ciliated protozoa, genes are transcribed in the macronucleus where the genome consists of 'gene-sized' linear DNA molecules. We have isolated clones of actin, tubulin and H4 histone macronuclear genes from Oxytricha nova, Stylonychia lemnae and Euplotes crassus in an effort to determine if they possess molecules of similar size for a given coding function, and also to determine the size range of non-coding DNA present on these molecules. Our results indicate that while the length of their non-coding DNA can vary slightly, both between different hypotrichs and within the gene family of a single organism, actin and tubulin macronuclear molecules are similarly sized. The sizes observed for these molecules support the hypothesis that each macronuclear molecule encodes a single gene. However, the H4 histone macronuclear molecules show a much wider size range and generally are much longer than necessary to encode the H4 histone. We therefore sequenced a 1700-bp H4 histone macronuclear molecule from O. nova to determine if it might possibly encode additional gene products. Sequence data reveals the presence of nine open reading frames (ORFs) greater than 100 bp in length; however, Northern hybridization analysis of the products of this DNA molecule reveals only a single transcript.

Actins↗
PubMed1989

Differential use of termination codons in ciliated protozoa.

Sequence analysis of genes in four species of ciliated protozoa and analysis of tRNAs in Tetrahymena has demonstrated that TAG and TAA encode glutamine or glutamic acid in these organisms and TGA is the only stop codon. Thus, it has generally been assumed that all ciliates use a nonuniversal genetic code in which TGA acts as the sole termination codon. We have sequenced the linear DNA molecules that carry an actin gene and a beta-tubulin gene from the ciliate Euplotes crassus. These genes are shown to use TAA as a termination codon based on homology to known actin and beta-tubulin gene sequences. In addition, we have sequenced a portion of the 3' terminus of the E. crassus H4 histone gene and show that it also uses TAA as a termination codon. These data indicate that the timing of genetic code changes in the ciliates must be reconsidered.

Actins↗
PubMed1976

Stability of RNA synthesized by the mouse oocyte during its major growth phase.

The RNA of growing mouse oocytes and ovulated ova was labeled by injection of a solution containing tritiated uridine into the ovarian bursa. The time course of incorporation into RNA by oocytes was followed by analysis of alkali-labile acid insoluble radioactivity and by autoradiography. The results show that most of the incorporation into RNA by growing oocytes takes place within one day of bursal injection of the precursor, reflecting the rapid fall of label in the acid soluble precursor pool. The RNA of growing oocytes of all sizes is unusually stable, at least 80% of the labeled RNA present two days after bursal injection being retained until ovulation 10 to 20 days later. The fraction of heterogeneous RNA in labeled RNA of ova was estimated as 20% by sucrose gradient analysis. It is likely that egg RNA is synthesized primarily during the period of oocyte growth one to three weeks before ovulation.

Animals↗
PubMedDate not supplied

Bradypneic, a new mutation in mice causing slow breathing, runting, and early death.

A new recessive mutation, bradypneic (bd), causes variable weight retardation beginning as early as 3 to 5 days. Severely affected mice die within the first 2 weeks; less severely affected mice may survive to weaning or to adulthood and may be fertile. Bradypneic mice tested at 3 weeks or older breathed at half the normal rate, but breathing was deeper and O2 consumption per unit of body surface was normal. No obstruction was found in the nasal passages, pharynx, trachea, or bronchi. The lungs were somewhat emphysematous and, probably in consequence, the right atrium was enlarged. The only other pathological conditions found were dilation of some of the distal tubules of the kidney and large amounts of gas in the stomach and intestines. The investigation did not reveal the cause of the breathing defect, but it is possible that the breathing defect is responsible for the emphysema, intestinal gas, small size, and early death. Extensive linkage tests have not yet revealed the chromosomal location of bd.

Animals↗